This is Info file pycrypt.info, produced by Makeinfo version 1.67 from
the input file pycrypt.texi.


File: pycrypt.info,  Node: Top,  Next: Introduction,  Prev: (dir),  Up: (dir)

   This document describes a package containing various cryptographic
modules available for the Python programming language.  It assumes you
have some basic knowledge about the Python language and about
cryptography in general.

* Menu:

* Introduction::                A dissertation on cryptography.
* Hash Functions::              Securely hashing data.
* Encryption Algorithms::       En/decrypting data.
* Public Key Algorithms::       Simple public-key cryptography.
* Odds and Ends::               Miscellaneous modules.
* Demo Programs::               Various demonstration programs.
* Extending::                   How to add new algorithms.

* Concept Index::


File: pycrypt.info,  Node: Introduction,  Next: Hash Functions,  Prev: Top,  Up: Top

Introduction
************

* Menu:

* Design Goals::
* Acknowledgements::


File: pycrypt.info,  Node: Design Goals,  Next: Acknowledgements,  Prev: Introduction,  Up: Introduction

Design Goals
============

   The Python cryptography modules are intended to provide a reliable
and stable base for writing Python programs that require cryptographic
functions.

   A central goal of the author's has been to provide a simple,
consistent interface for similar classes of algorithms.  For example,
all block cipher objects have the same methods and return values, and
support the same feedback modes; hash functions have a different
interface, but it too is consistent over all the hash functions
available.  Individual modules also define variables to help you write
Python code that doesn't depend on the algorithms used; for example,
each block cipher module defines a variable that gives the algorithm's
block size.  This is intended to make it easy to replace old algorithms
with newer, more secure ones.  If you're given a bit of
portably-written Python code that uses the DES encryption algorithm,
you should be able to use IDEA instead by simply changing `from
Crypto.Cipher import DES' to `from Crypto.Cipher import idea', and
changing all references to `DES.new()' to `IDEA.new()'.  It's also
fairly simple to write your own modules that mimic this interface, thus
letting you use combinations or permutations of algorithms.

   Some modules are implemented in C for performance; others are
written in Python for ease of modification.  Generally, low-level
functions like ciphers and hash functions are written in C, while less
speed-critical functions have been written in Python.  This division
may change in future releases.  When speeds are quoted in this
document, they were measured on a AMD K6/200 running Linux.  The exact
speeds will obviously vary with different machines and different
compilers, but they provide a basis for comparing algorithms.
Currently the cryptographic implementations are acceptably fast, but
not spectacularly good.  I welcome any suggestions or patches for
faster code.

   If you live outside of Canada or the US, please do not attempt to
download it from a North American FTP site; you may get the site's
maintainer in trouble.  Documentation is not covered by the ITAR
regulations, and can be freely sent anywhere in the world.

   I have placed the code under no restrictions; you can redistribute
the code freely or commercially, in its original form or with any
modifications you make, subject to whatever local laws may apply in your
jurisdiction.  Note that you still have to come to some agreement with
the holders of any patented algorithms you're using.  If you're
intensively using these modules, please tell me about it; there's little
incentive for me to work on this package if I don't know of anyone using
it.

   I also make no guarantees as to the usefulness, correctness, or
legality of these modules, nor does their inclusion constitute an
endorsement of their effectiveness.  Many cryptographic algorithms are
patented; inclusion in this package does not necessarily mean you are
allowed to incorporate them in a product and sell it.  Some of these
algorithms may have been cryptanalyzed, and may no longer be secure.
While I will include commentary on the relative security of the
algorithms in the sections entitled "Security Notes", there may be more
recent analyses I'm not aware of.  (Or maybe I'm just clueless.)  If
you're implementing an important system, don't just grab things out of
a toolbox and put them together; do some research first.  On the other
hand, if you're just interested in keeping your co-workers or your
relatives out of your files, any of the components here could be used.

   This document is very much a work in progress.  If you have any
questions, comments, complaints, or suggestions, please send them to me
at <akuchling@acm.org>.


File: pycrypt.info,  Node: Acknowledgements,  Prev: Design Goals,  Up: Introduction

Acknowledgements
================

   Much of the code that actually implements the various cryptographic
algorithms was not written by me.  I'd like to thank all the people who
implemented them, and released their work under terms which allowed me
to use their code.  The individuals are credited in the relevant
chapters of this documentation.  Bruce Schneier's book `Applied
Cryptography' was also very useful in writing this toolkit; I highly
recommend it if you're interested in learning more about cryptography.
Mr. Schneier also has a Web site at `http://www.counterpane.com'.

   Good luck with your cryptography hacking!

   A.M.K.

   <akuchling@acm.org>

   Washington, DC, USA

   January 1998


File: pycrypt.info,  Node: Hash Functions,  Next: Encryption Algorithms,  Prev: Introduction,  Up: Top

`Crypto.Hash': Hash Functions
*****************************

   Hash functions take arbitrary strings as input, and produce an output
of fixed size that is dependent on the input; it should never be
possible to derive the input data given only the hash function's
output.  One simple hash function consists of simply adding together
all the bytes of the input, and taking the result modulo 256.  For a
hash function to be cryptographically secure, it must be very difficult
to find two messages with the same hash value, or to find a message
with a given hash value.  The simple additive hash function fails this
criterion miserably; the hash functions described below do not.
Examples of cryptographically secure hash functions include MD2, MD5,
SHA, and HAVAL.

   Hash functions can be used simply as a checksum, or, in association
with a public-key algorithm, can be used to implement digital
signatures.

   The hashing algorithms currently implemented are listed in the
following table:

Hash function
     Digest length

MD2
     128 bits

MD4
     128 bits

MD5
     128 bits

SHA
     160 bits

HAVAL
     Variable size: 128, 160, 192, 224, or 256 bits.

   All hashing modules share the same interface.  After importing a
given hashing module, call the `new()' function to create a new hashing
object. (In older versions of the Python interpreter, the `md5()'
function was used to perform this task.  If you're modifying an old
script, you should change any calls to `md5()' to use `new()' instead.)
You can now feed arbitrary strings into the object, and can ask for the
hash value at any time.  The `new()' function can also be passed an
optional string parameter, which will be hashed immediately.

   Hash function modules define one variable:

 - Variable of hashing modules: digestsize
     An integer value; the size of the digest produced by the hashing
     objects.  You could also obtain this value by creating a sample
     object, and taking the length of the digest string it returns, but
     using `digestsize' is faster.

   The methods for hashing objects are always the following:

 - Method on hashing objects: copy ()
     Return a separate copy of this hashing object.  An `update' to this
      copy won't affect the original object.

 - Method on hashing objects: digest ()
     Return the hash value of this hashing object, as a string
     containing 8-bit data.  The object is not altered in any way by
     this function; you can continue updating the object after calling
     this function.

 - Method on hashing objects: digest ()
     Return the hash value of this hashing object, as a string
     containing the digest data as hexadecimal digits.  The resulting
     string will be twice as long as that returned by `digest()'.  The
     object is not altered in any way by this function; you can
     continue updating the object after calling this function.

 - Method on hashing objects: update (ARG)
     Update this hashing object with the string ARG.

   Here's an example, using RSA Data Security's MD5 algorithm:

     >>> from Crypto.Hash import MD5
     >>> m = MD5.new()
     >>> m.update('abc')
     >>> m.digest()
     '\220\001P\230<\322O\260\326\226?}(\341\177r'

   Or, more compactly:
     >>> MD5.new('abc').digest()
     '\220\001P\230<\322O\260\326\226?}(\341\177r'

* Menu:

* Algorithm-specific Notes for Hash Functions::
* Security Notes for Hash Functions::
* Credits for Hash Functions::


File: pycrypt.info,  Node: Algorithm-specific Notes for Hash Functions,  Next: Security Notes for Hash Functions,  Prev: Hash Functions,  Up: Hash Functions

Algorithm-specific Notes for Hash Functions
===========================================

   HAVAL provides a variable-size digest, and allows for a variable
number of rounds.  It's believed that increasing the number of rounds
increases the security; at least, I don't know of any results to the
contrary.  The `HAVAL.new()' accordingly has two keyword arguments,
`rounds' and `digestsize'.  `rounds' can be 3, 4, or 5, and has a
default value of 5.  `digestsize' can be 128, 160, 192, 224, or 256
bits, and has a default value of 256.


File: pycrypt.info,  Node: Security Notes for Hash Functions,  Next: Credits for Hash Functions,  Prev: Algorithm-specific Notes for Hash Functions,  Up: Hash Functions

Security Notes
==============

   Hashing algorithms are broken when it's easy to compute a string
that produces a given hash value, or to find two messages that produce
the same hash value. Consider an example where Alice and Bob are using
digital signatures to sign a contract.  Alice computes the hash value
of the text of the contract and signs it.  Bob could then compute a
different contract that has the same hash value, and it would appear
that Alice has signed that bogus contract; she'd have no way to prove
otherwise.  Finding such a message by brute force takes `pow(2, b-1)'
operations, where the hash function produces *b*-bit hashes.

   If Bob can only find two messages with the same hash value but can't
choose the resulting hash value, he can look for two messages with
different meanings, such as "I will mow Bob's lawn for $10" and "I owe
Bob $1,000,000", and ask Alice to sign the first, innocuous contract.
This attack is easier for Bob, since finding two such messages by brute
force will take `pow(2, b/2)' operations on average.  However, Alice
can protect herself by changing the protocol; she can simply append a
random string to the contract before hashing and signing it; the random
string can then be kept with the signature.

   None of the algorithms implemented here have been completely broken.
There are no attacks on MD2, but it's rather slow at 424 K/sec.  MD4 is
faster at 11710 K/sec but there have been some partial attacks on it.
MD4 operates in three iterations of a basic mixing operation; two of the
three rounds have been cryptanalyzed, but the attack can't be extended
to the full algorithm.  MD5 is a strengthened version of MD4 with four
rounds; an attack against one round has been found.  XXX Dobbertin's
attack.  Because MD5 is more commonly used, the implementation is
better optimized and thus faster on x86 processors (19303 K/sec).  MD4
may be faster than MD5 when other processors and compilers are used.

   All the MD algorithms produce 128-bit hashes; SHA produces a larger
160-bit hash, and there are no known attacks against it.  The first
version of SHA had a weakness which was later corrected; the code used
here implements the second, corrected, version.  It operates at 7192
K/sec.

   HAVAL is a variable-size hash function; it can generate hash values
that are 128, 160, 192, 224, or 256 bits in size, and can use 3, 4, or 5
rounds.  5-round HAVAL runs at 2381 K/sec.


File: pycrypt.info,  Node: Credits for Hash Functions,  Prev: Security Notes for Hash Functions,  Up: Hash Functions

Credits
=======

   The MD2, MD4, and HAVAL implementations were written by A.M.
Kuchling, and the MD5 code was implemented by Colin Plumb.  The SHA
code was originally written by Peter Gutmann.


File: pycrypt.info,  Node: Encryption Algorithms,  Next: Public Key Algorithms,  Prev: Hash Functions,  Up: Top

`Crypto.Cipher': Encryption Algorithms
**************************************

   Encryption algorithms transform their input data (called
"plaintext") in some way that is dependent on a variable "key",
producing "ciphertext"; this transformation can easily be reversed, if
(and, hopefully, only if) one knows the key.  The key can be varied by
the user or application, chosen from some very large space of possible
keys.

   For a secure encryption algorithm, it should be very difficult to
determine the original plaintext without knowing the key; usually, no
clever attacks on the algorithm are known, so the only way of breaking
the algorithm is to try all possible keys. Since the number of possible
keys is usually of the order of 2 to the power of 56 or 128, this is not
a serious threat, although 2 to the power of 56 is now considered
insecure in the face of custom-built parallel computers and distributed
key guessing efforts.

   "Block ciphers" take multibyte inputs of a fixed size (frequently 8
or 16 bytes long) and encrypt them.  Block ciphers can be operated in
various modes.  The simplest is Electronic Code Book (or ECB) mode.  In
this mode, each block of plaintext is simply encrypted to produce the
ciphertext.  This mode can be dangerous, because many files will
contain patterns greater than the block size; for example, the comments
in a C program may contain long strings of asterisks intended to form a
box.  All these identical blocks will encrypt to identical ciphertext;
an adversary may be able to use this structure to obtain some
information about the text.

   To eliminate this weakness, there are various feedback modes, where
the plaintext is combined with the previous ciphertext before
encrypting; this eliminates any such structure.  One mode is Cipher
Block Chaining (CBC mode); another is Cipher FeedBack (CFB mode).   CBC
mode still encrypts in blocks, and thus is only slightly slower than
ECB mode.  CFB mode encrypts on a byte-by-byte basis, and is much
slower than either of the other two modes.  The chaining feedback modes
require an initialization value to start off the encryption; this is a
string of the same length as the ciphering algorithm's block size, and
is passed to the `new()' function.

   There is also a special PGP mode, which is a variant of CFB used by
the PGP program.  While you can use it in non-PGP programs, it's quite
non-standard.

   The currently available block ciphers are listed in the following
table, and are available in the `Crypto.Cipher' package:

Cipher
     Key Size/Block Size

ARC2
     Variable/8 bytes

Blowfish
     Variable/8 bytes

CAST
     Variable/8 bytes

DES
     8 bytes/8 bytes

DES3 (Triple DES)
     16 bytes/8 bytes

Diamond
     Variable/16 bytes

IDEA
     16 bytes/8 bytes

RC5
     Variable/8 bytes

   In a strict formal sense, "stream ciphers" encrypt data bit-by-bit;
practically, stream ciphers work on a character-by-character basis.
Stream ciphers use exactly the same interface as block ciphers, with a
block length that will always be 1; this is how block and stream
ciphers can be distinguished.  The only feedback mode available for
stream ciphers is ECB mode.

   The currently available stream ciphers are listed in the following
table:

Cipher
Key Size
ARC4
Variable
Sapphire
Variable
   ARC4 is short for `Alleged RC4'.  The real RC4 algorithm is
proprietary to RSA Data Security Inc.  In September of 1994, someone
posted C code to both the Cypherpunks mailing list and to the Usenet
newsgroup `sci.crypt', claiming that it implemented the RC4 algorithm.
This posted code is what I'm calling Alleged RC4, or ARC4 for short.  I
don't know if ARC4 is in fact RC4, but ARC4 has been subjected to
scrutiny on the Cypherpunks mailing list and elsewhere, and does not
seem to be easily breakable.  The legal issues surrounding the use of
ARC4 are unclear, but be aware that it hasn't been subject to much
scrutiny, and may have some critical flaw that hasn't yet been
discovered.  The same is true of ARC2, which was posted in January,
1996.

   An example usage of the DES module:
     >>> from Crypto.Cipher import DES
     >>> obj=DES.new('abcdefgh', DES.ECB)
     >>> plain="Guido van Rossum is a space alien."
     >>> len(plain)
     34
     >>> obj.encrypt(plain)
     Traceback (innermost last):
       File "<stdin>", line 1, in ?
     ValueError: Strings for DES must be a multiple of 8 in length
     >>> ciph=obj.encrypt(plain+'XXXXXX')
     >>> ciph
     '\021,\343Nq\214DY\337T\342pA\372\255\311s\210\363,\300j\330\250\312\347\342I\3215w\03561\303dgb/\006'
     >>> obj.decrypt(ciph)
     'Guido van Rossum is a space alien.XXXXXX'

   All cipher algorithms share a common interface.  After importing a
given module, there is exactly one function and two variables available.

 - Function of encryption modules: new
     Returns a ciphering object, using KEY and feedback mode MODE.  If
     MODE is CBC or CFB, IV must be provided, and must be a string of
     the same length as the block size.  Some algorithms support
     additional keyword arguments to this function; see the
     "Algorithm-specific Notes for Encryption Algorithms" section below
     for the details.

 - Variable of encryption modules: blocksize
     An integer value; the size of the blocks encrypted by this module.
     Strings passed to the `encrypt' and `decrypt' functions must be a
     multiple of this length.  For stream ciphers, `blocksize' will be
     1.

 - Variable of encryption modules: keysize
     An integer value; the size of the keys required by this module.  If
     `keysize' is zero, then the algorithm accepts arbitrary-length
     keys.  You cannot pass a key of length 0 (that is, the null string
     `''' as such a variable-length key.

   All cipher objects have one attribute:

 - Attribute of encryption objects: IV
     Contains the initial value which will be used to start a cipher
     feedback mode.  After encrypting or decrypting a string, this value
     will reflect the modified feedback text; it will always be one
     block in length.  It is read-only, and cannot be assigned a new
     value.

   All ciphering objects have the following methods:

 - Method on encryption objects: decrypt (STRING)
     Decrypts STRING, using the key-dependent data in the object, and
     with the appropriate feedback mode.  The string's length must be
     an exact multiple of the algorithm's block size.  Returns a string
     containing the plaintext.

 - Method on encryption objects: encrypt (STRING)
     Encrypts a non-null STRING, using the key-dependent data in the
     object, and with the appropriate feedback mode.  The string's
     length must be an exact multiple of the algorithm's block size;
     for stream ciphers, the string can be of any length.  Returns a
     string containing the ciphertext.

* Menu:

* Algorithm-specific Notes for Encryption Algorithms::
* Security Notes for Encryption Algorithms::
* Credits for Encryption Algorithms::


File: pycrypt.info,  Node: Algorithm-specific Notes for Encryption Algorithms,  Next: Security Notes for Encryption Algorithms,  Prev: Encryption Algorithms,  Up: Encryption Algorithms

Algorithm-specific Notes for Encryption Algorithms
==================================================

   The Diamond block cipher allows you to select the number of rounds to
apply, ranging from 5 to 15 (inclusive.)  This is set via the `rounds'
keyword argument to the `new()' function; the default value is 8 rounds.

   RC5 has even more parameters; see Ronald Rivest's paper for the
implementation details.  The keyword parameters are:

   * `version': The version of the RC5 algorithm to use; currently the
     only legal value is `0x10' for RC5 1.0.

   * `wordsize': The word size to use; 16 or 32 are the only legal
     values.  (A larger word size is better, so usually 32 will be
     used.  16-bit RC5 is probably only of academic interest.)

   * `rounds': The number of rounds to apply, the larger the more
     secure: this can be any value from 0 to 255, so you will have to
     choose a value balanced between speed and security.


File: pycrypt.info,  Node: Security Notes for Encryption Algorithms,  Next: Credits for Encryption Algorithms,  Prev: Algorithm-specific Notes for Encryption Algorithms,  Up: Encryption Algorithms

Security Notes
==============

   Encryption algorithms can be broken in several ways.  If you have
some ciphertext and know (or can guess) the corresponding plaintext,
you can simply try every possible key in a "known-plaintext" attack.
Or, it might be possible to encrypt text of your choice using an
unknown key; for example, you might mail someone a message intending it
to be encrypted and forwarded to someone else.  This is a
"chosen-plaintext" attack, which is particularly effective if it's
possible to choose plaintexts that reveal something about the key when
encrypted.

   DES (1455 K/sec) has a 56-bit key; this is starting to become too
small for safety.  It has been estimated that it would only cost
$1,000,000 to build a custom DES-cracking machine that could find a key
in 3 hours.  A chosen-ciphertext attack using the technique of "linear
cryptanalysis" can break DES in `pow(2, 43)' steps.  However, unless
you're encrypting data that you want to be safe from major governments,
DES will be fine. DES3 (509 K/sec) uses three DES encryptions for
greater security and a 112-bit or 168-bit key, but is correspondingly
slower.

   There are no publicly known attacks against IDEA (809 K/sec), and
it's been around long enough to have been examined.  There are no known
attacks against ARC2 (1112 K/sec), ARC4 (2852 K/sec), Blowfish (2229
K/sec), CAST (1053 K/sec), Diamond (777 K/sec), RC5 (1365 K/sec), or
Sapphire (1468 K/sec), but they're all relatively new algorithms and
there hasn't been time for much analysis to be performed; use them for
serious applications only after careful research.


File: pycrypt.info,  Node: Credits for Encryption Algorithms,  Prev: Security Notes for Encryption Algorithms,  Up: Encryption Algorithms

Credits
=======

   The code for Blowfish was written by Bryan Olson, partially based on
a previous implementation by Bruce Schneier, who also invented the
algorithm; the Blowfish algorithm has been placed in the public domain
and can be used freely.  (See `http://www.counterpane.com' for more
information about Blowfish.)  The CAST implementation was written by
Wim Lewis.  The DES implementation was written by Eric Young, and the
IDEA implementation by Colin Plumb. The RC5 implementation was written
by A.M. Kuchling.

   The Alleged RC4 code was posted to the `sci.crypt' newsgroup by an
unknown party, and re-implemented by A.M. Kuchling.  The Sapphire stream
cipher was developed by Michael P. Johnson, and is in the public domain;
the implementation used here was written by A.M. Kuchling and is based
on Johnson's code.


File: pycrypt.info,  Node: Public Key Algorithms,  Next: Odds and Ends,  Prev: Encryption Algorithms,  Up: Top

`Crypto.PublicKey': Public Key Algorithms
*****************************************

   So far, the encryption algorithms described have all been "private
key" ciphers.  That is, the same key is used for both encryption and
decryption, so all correspondents must know it.  This poses a problem:
you may want encryption to communicate sensitive data over an insecure
channel, but how can you tell your correspondent what the key is?  You
can't just e-mail it to her because the channel is insecure.  One
solution is to arrange the key via some other way: over the phone or by
meeting in person.

   Another solution is to use "public key" cryptography.  In a public
key system, there are two different keys: one for encryption and one for
decryption.  The encryption key can be made public by listing it in a
directory or mailing it to your correspondent, while you keep the
decryption key secret.  Your correspondent then sends you data encrypted
with your public key, and you use the private key to decrypt it.  While
the two keys are related, it's very difficult to derive the private key
given only the public key; however, deriving the private key is always
possible given enough time and computing power.  This makes it very
important to pick keys of the right size: large enough to be secure, but
small enough to be applied fairly quickly.

   Many public key algorithms can also be used to sign messages; simply
run the message to be signed through a decryption with your private key
key.  Anyone receiving the message can encrypt it with your publicly
available key and read the message.  Some algorithms do only one thing,
others can both encrypt and authenticate.

   The currently available public key algorithms are listed in the
following table:

Algorithm
     Capabilities

RSA
     Encryption, authentication/signatures

ElGamal
     Encryption, authentication/signatures

DSA
     Authentication/signatures

qNEW
     Authentication/signatures

   Many of these algorithms are patented.  Before using any of them in a
commercial product, consult a patent attorney; you may have to arrange
a license with the patent holder.

   An example of using the RSA module to sign a message:
     >>> from Crypto.Hash import MD5
     >>> from Crypto.PublicKey import RSA
     >>> RSAkey=RSA.generate(384, randfunc)   # This will take a while...
     >>> hash=MD5.new(plaintext).digest()
     >>> signature=RSAkey.sign(hash, "")
     >>> signature   # Print what an RSA sig looks like--you don't really care.
     ('\021\317\313\336\264\315' ...,)
     >>> RSAkey.verify(hash, signature)     # This sig will check out
     1
     >>> RSAkey.verify(hash[:-1], signature)# This sig will fail
     0

   Public key modules make the following functions available:

 - Function of public-key modules: construct
     Constructs a key object from a tuple of data.  This is
     algorithm-specific; look at the source code for the details.  (To
     be documented later.)

 - Function of public-key modules: generate
     Generate a fresh public/private key pair.  SIZE is a
     algorithm-dependent size parameter; the larger it is, the more
     difficult it will be to break the key.  Safe key sizes vary from
     algorithm to algorithm; you'll have to research the question and
     decide on a suitable key size for your application.  `randfunc' is
     a random number generation function; it should accept a single
     integer N and return a string of random data N bytes long.  You
     should always use a cryptographically secure random number
     generator, such as the one defined in the `randpool' module;
     *don't* just use the current time and the `whrandom' module.

     PROGRESS_FUNC is an optional function that will be called with a
     short string containing the key parameter currently being
     generated; it's useful for interactive applications where a user
     is waiting for a key to be generated.

   If you want to interface with some other program, you will have to
know the details of the algorithm being used; this isn't a big loss.
If you don't care about working with non-Python software, simply use the
`pickle' module when you need to write a key or a signature to a file.
It's portable across all the architectures that Python supports, and
it's simple to use.

   Public key objects always support the following methods.  Some of
them may raise exceptions if their functionality is not supported by the
algorithm.

 - Method on public-key objects: canencrypt ()
     Returns true if the algorithm is capable of encrypting and
     decrypting data; returns false otherwise.  To test if a given key
     object can sign data, use `key.canencrypt() and key.hasprivate()'.

 - Method on public-key objects: cansign ()
     Returns true if the algorithm is capable of signing data; returns
     false otherwise.  To test if a given key object can sign data, use
     `key.cansign() and key.hasprivate()'.

 - Method on public-key objects: decrypt (TUPLE)
     Decrypts TUPLE with the private key, returning another string.
     This requires the private key to be present, and will raise an
     exception if it isn't present.  It will also raise an exception if
     STRING is too long.

 - Method on public-key objects: encrypt (STRING, K)
     Encrypts STRING with the private key, returning a tuple of
     strings; the length of the tuple varies from algorithm to
     algorithm.  K should be a string of random data that is as long as
     possible.  Encryption does not require the private key to be
     present inside the key object.  It will raise an exception if
     STRING is too long.  For ElGamal objects, the value of K expressed
     as a big-endian integer must be relatively prime to `self.p-1'; an
     exception is raised if it is not.

 - Method on public-key objects: hasprivate ()
     Returns true if the key object contains the private key data, which
     will allow decrypting data and generating signatures.  Otherwise
     this returns false.

 - Method on public-key objects: publickey ()
     Returns a new public key object that doesn't contain the private
     key data.

 - Method on public-key objects: sign (STRING, K)
     Sign STRING, returning a signature, which is just a tuple; in
     theory the signature may be made up of any Python objects at all;
     in practice they'll be either strings or numbers.  K should be a
     string of random data that is as long as possible.  Different
     algorithms will return tuples of different sizes.  `sign()' raises
     an exception if STRING is too long.  For ElGamal objects, the value
     of K expressed as a big-endian integer must be relatively prime to
     `self.p-1'; an exception is raised if it is not.

 - Method on public-key objects: size ()
     Returns the maximum size of a string that can be encrypted or
     signed, measured in bits.  String data is treated in big-endian
     format; the most significant byte comes first.  (This seems to be
     a de facto standard for cryptographical software.)  If the size is
     not a multiple of 8, then some of the high order bits of the first
     byte must be zero.  Usually it's simplest to just divide the size
     by 8 and round down.

 - Method on public-key objects: verify (STRING, SIGNATURE)
     Returns true if the signature is valid, and false otherwise.
     STRING is not processed in any way; `verify' does not run a hash
     function over the data, but you can easily do that yourself.

* Menu:

* The ElGamal and DSA algorithms::
* Security Notes for Public-key Algorithms::


File: pycrypt.info,  Node: The ElGamal and DSA algorithms,  Next: Security Notes for Public-key Algorithms,  Prev: Public Key Algorithms,  Up: Public Key Algorithms

The ElGamal and DSA algorithms
==============================

   For RSA, the K parameters are unused; if you like, you can just pass
empty strings.  The ElGamal and DSA algorithms require a real K value
for technical reasons; see Schneier's book for a detailed explanation
of the respective algorithms.  This presents a possible hazard that can
inadvertently reveal the private key.  Without going into the
mathematical details, the danger is as follows. K is never derived or
needed by others; theoretically, it can be thrown away once the
encryption or signing operation is performed.  However, revealing K for
a given message would enable others to derive the secret key data;
worse, reusing the same value of K for two different messages would
also enable someone to derive the secret key data.  An adversary could
intercept and store every message, and then try deriving the secret key
from each pair of messages.

   This places implementors on the horns of a dilemma.  On the one hand,
you want to store the K values to avoid reusing one; on the other hand,
storing them means they could fall into the hands of an adversary.  One
can randomly generate K values of a suitable length such as 128 or 144
bits, and then trust that the random number generator probably won't
produce a duplicate anytime soon.  This is an implementation decision
that depends on the desired level of security and the expected usage
lifetime of a private key.  I cannot choose and enforce one policy for
this, so I've added the K parameter to the `encrypt' and `sign'
functions.  You must choose K by generating a string of random data;
for ElGamal, when interpreted as a big-endian number (with the most
significant byte being the first byte of the string), K must be
relatively prime to `self.p-1'; any size will do, but brute force
searches would probably start with small primes, so it's probably good
to choose fairly large numbers.  It might be simplest to generate a
prime number of a suitable length using the `Crypto.Util.number' module.


File: pycrypt.info,  Node: Security Notes for Public-key Algorithms,  Prev: The ElGamal and DSA algorithms,  Up: Public Key Algorithms

Security Notes for Public-key Algorithms
========================================

   Any of these algorithms can be trivially broken; for example, RSA
can be broken by factoring the modulus *n* into its two prime factors.
This is easily done by the following code:

     for i in range(2, n):
         if (n%i)==0: print i, 'is a factor' ; break

   However, *n* is usually a few hundred bits long, so this simple
program wouldn't find a solution before the universe comes to an end.
Smarter algorithms can factor numbers more quickly, but it's still
possible to choose keys so large that they can't be broken in a
reasonable amount of time.  For ElGamal and DSA, discrete logarithms are
used instead of factoring, but the principle is the same.

   Safe key sizes depend on the current state of computer science and
technology.  At the moment, one can roughly define three levels of
security: low-security commercial, high-security commercial, and
military-grade.  For RSA, these three levels correspond roughly to 512,
768, and 1024 bit-keys.  For ElGamal and DSA, the key sizes should be
somewhat larger for the same level of security, around 768, 1024, and
1536 bits.


File: pycrypt.info,  Node: Odds and Ends,  Next: Demo Programs,  Prev: Public Key Algorithms,  Up: Top

`Crypto.Util': Odds and Ends
****************************

   This chapter contains all the modules that don't fit into any of the
other chapters.

* Menu:

* number module::               Number-theoretic operations
* randpool module::             Random number generation.
* RFC1751 module::              Converting binary keys to/from English words


File: pycrypt.info,  Node: number module,  Next: randpool module,  Prev: Odds and Ends,  Up: Odds and Ends

`Crypto.Util.number'
====================


File: pycrypt.info,  Node: randpool module,  Next: RFC1751 module,  Prev: number module,  Up: Odds and Ends

`Crypto.Util.randpool'
======================

   For cryptographic purposes, ordinary random number generators are
frequently insufficient, because if some of their output is known, it is
frequently possible to derive the generator's future (or past) output.
This is obviously a Bad Thing; given the generator's state at some point
in time, someone could try to derive any keys generated using it.  The
solution is to use strong encryption or hashing algorithms to generate
successive data; this makes breaking the generator as difficult as
breaking the algorithms used.

   Understanding the concept of "entropy" is important for using the
random number generator properly.  In the sense we'll be using it,
entropy measures the amount of randomness; the usual unit is in bits.
So, a single random bit has an entropy of 1 bit; a random byte has an
entropy of 8 bits.  Now consider a one-byte field in a database
containing a person's sex, represented as a single character `M' or `F'.
What's the entropy of this field?  Since there are only two possible
values, it's not 8 bits, but two; if you were trying to guess the value,
you wouldn't have to bother trying `Q' or `@'.

   Now imagine running that single byte field through a hash function
that produces 128 bits of output.  Is the entropy of the resulting hash
value 128 bits?  No, it's still just 1 bit.  The entropy is a measure
of how many possible states of the data exist.  For English text, the
entropy of a five-character string is not 40 bits; it's somewhat less,
because not all combinations would be seen.  `Guido' is a possible
string, as is `In th'; `zJwvb' is not.

   The relevance to random number generation?  We want enough bits of
entropy to avoid making an attack on our generator possible.  An
example: One computer system had a mechanism which generated nonsense
passwords for its users.  This is a good idea, since it would prevent
people from choosing their own name or some other easily guessed string.
Unfortunately, the random number generator used only had 65536 states,
which meant only 65536 different passwords would ever be generated, and
it was easily to compute all the possible passwords and try them.  The
entropy of the random passwords was far too low.  By the same token, if
you generate an RSA key with only 32 bits of entropy available, there
are only about 4.2 billion keys you could have generated, and an
adversary could compute them all to find your private key.  See RFC
1750: "Randomness Recommendations for Security" for an interesting
discussion of the issues related to random number generation.

   The `randpool' module implements a strong random number generator in
the `RandomPool' class.  The internal state consists of a string of
random data, which is returned as callers request it.  The class keeps
track of the number of bits of entropy left, and provides a function to
add new random data; this data can be obtained in various ways, such as
by using the variance in a user's keystroke timings.

 - Class of `randpool': RandomPool
     An object of the `RandomPool' class can be created without
     parameters if desired.  NUMBYTES sets the number of bytes of
     random data in the pool. CIPHER and HASH are strings containing
     the module name of the encryption algorithm and the hash function
     to use in stirring the random data.  The default values of these
     parameters are 128 bytes (or 1024 bits), `'IDEA'', and `'MD5''.

   `RandomPool' objects define the following variables and methods:

 - Method on `RandomPool' objects: addEvent (TIME, [STRING])
     Adds an event to the random pool.  TIME should be set to the
     current system time, measured at the highest resolution available.
     STRING can be a string of data that will be XORed into the pool,
     and can be used to increase the entropy of the pool.  For example,
     if you're encrypting a document, you might use the hash value of
     the document; an adversary presumably won't have the plaintext of
     the document, and thus won't be able to use this information to
     break the generator.

   The return value is the value of `self.entropy' after the data has
been added.  The function works in the following manner: the time
between successive calls to the `addEvent' method is determined, and
the entropy of the data is guessed; the larger the time between calls,
the better.  The system time is then read and added to the pool, along
with the STRING parameter, if present.  The hope is that the low-order
bits of the time are effectively random.  In an application, it is
recommended that `addEvent()' be called as frequently as possible, with
whatever random data can be found.

 - Variable of `RandomPool' objects: bits
     A constant integer value containing the number of bits of data in
     the pool, equal to the `bytes' variable multiplied by 8.

 - Variable of `RandomPool' objects: bytes
     A constant integer value containing the number of bytes of data in
     the pool.

 - Variable of `RandomPool' objects: entropy
     An integer value containing the number of bits of entropy
     currently in the pool.  The value is incremented by the
     `addEvent()' method, and decreased by the `getBytes' method.

 - Method on `RandomPool' objects: getBytes (NUM)
     Returns a string containing NUM bytes of random data, and
     decrements the amount of entropy available.  It is not an error to
     reduce the entropy to zero, or to call this function when the
     entropy is zero.  This simply means that, in theory, enough random
     information has been extracted to derive the state of the
     generator.  It is the caller's responsibility to monitor the
     amount of entropy remaining and decide whether it is sufficent for
     secure operation.

 - Method on `RandomPool' objects: stir ()
     Scrambles the random pool using the previously chosen encryption
     and hash function.  An adversary may attempt to learn or alter the
     state of the pool in order to affect its future output; this
     function destroys the existing state of the pool in a
     non-reversible way.  It is recommended that `stir()' be called
     before and after using the `RandomPool' object.  Even better,
     several calls to `stir()' can be interleaved with calls to
     `addEvent()'.

   The `KeyboardRandomPool' class is a subclass of `RandomPool' that
adds the capability to save and load the pool from a disk file, and
provides a method to obtain random data from the keyboard.

 - Class of `randpool': RandomPool
     The path given in FILENAME will be automatically opened, and an
     existing random pool read; if no such file exists, the pool will be
     initialized as usual.  If omitted, the filename defaults to the
     empty string, which will prevent it from being saved to a file.
     The other arguments are identical to those for the `RandomPool'
     constructor.

 - Method on `RandomPool' objects: randomize ()
     (Unix systems only)  Obtain random data from the keyboard.  This
     works by prompting the user to hit keys at random, and then using
     the keystroke timings (and also the actual keys pressed) to add
     entropy to the pool.  This works similarly to PGP's random pool
     mechanism.

 - Method on `RandomPool' objects: save ()
     Opens the file named by the `filename' attribute, and saves the
     random data into the file using the `pickle' module.


File: pycrypt.info,  Node: RFC1751 module,  Prev: randpool module,  Up: Odds and Ends

`Crypto.Util.RFC1751'
=====================

   The keys for private-key algorithms should be arbitrary binary data.
Many systems err by asking the user to enter a password, and then using
the password as the key.  This limits the space of possible keys, as
each key byte is constrained within the range of possible ASCII
characters, 32-127, instead of the whole 0-255 range possible with
ASCII.  Unfortunately, it's difficult for humans to remember 16 or 32
hex digits.

   One solution is to request a lengthy passphrase from the user, and
then run it through a hash function such as SHA or MD5.  Another
solution is discussed in RFC 1751, "A Convention for Human-Readable
128-bit Keys", by Daniel L. McDonald.  Binary keys are transformed into
a list of short English words that should be easier to remember.  For
example, the hex key EB33F77EE73D4053 is transformed to "TIDE ITCH SLOW
REIN RULE MOT".

 - Function: Key2English (KEY)
     Accepts a string of arbitrary data KEY, and returns a string
     containing uppercase English words separated by spaces.  KEY's
     length must be a multiple of 8.

 - Function: English2Key (STRING)
     Accepts STRING containing English words, and returns a string of
     binary data representing the key.  Words must be separated by
     whitespace, and can be any mixture of uppercase and lowercase
     characters.  6 words are required for 8 bytes of key data, so the
     number of words in STRING must be a multiple of 6.


File: pycrypt.info,  Node: Demo Programs,  Next: Extending,  Prev: Odds and Ends,  Up: Top

The Demonstration Programs
**************************

   The Python cryptography modules comes with various demonstration
programs, located in the `Demo/' directory.  None of them is
particularly well-finished, or suitable for serious use.  Rather,
they're intended to illustrate how the toolkit is used, and to provide
some interesting possible uses.  Feel free to incorporate the code (or
modifications of it) into your own programs.

* Menu:

* cipher Demo::                 File encryption program.
* Secure import::               A secure `import' statement.


File: pycrypt.info,  Node: cipher Demo,  Next: Secure import,  Prev: Demo Programs,  Up: Demo Programs

Demo 1: `cipher'
================

   `cipher' encrypts and decrypts files.  On most Unix systems, the
`crypt' program uses a variant of the Enigma cipher.  This is not
secure, and there exists a freely available program called "Crypt
Breaker's Workbench" which helps in breaking the cipher if you have
some knowledge of the encrypted data.

   `cipher' is a more secure file encryption program.  Simply list the
names of the files to be encrypted on the command line.  `cipher' will
go through the list and encrypt or decrypt them; `cipher' can recognize
files it has previously encrypted.  The ciphertext of a file is placed
in a file of the same name with '`.cip'' appended; the original file is
not deleted, since I'm not sure that all errors during operation are
caught, and I don't want people to accidentally erase important files.

   There are two command-line options: `-c' and `-k'.  Both of them
require an argument.  `-c CIPHERNAME' uses the given encryption
algorithm CIPHERNAME; for example, `-c des' will use the DES algorithm.
The name should be the same as an available module name; thus it
should be in lowercase letters.  The default cipher is IDEA.

   `-k KEY' can be used to set the encryption key to be used.  Note
that on a multiuser Unix system, the `ps' command can be used to view
the arguments of commands executed by other users, so this is insecure;
if you're the only user (say, on your home computer running Linux) you
don't have to worry about this.  If no key is set on the command line,
`cipher' will prompt the user to input a key on standard input.

Technical Details
-----------------

   The encrypted file is not pure ciphertext.  First comes a magic
string; this is currently the sequence `ctx' and a byte containing 1
(the version number of `cipher').  This is followed by the
null-terminated name of the encryption algorithm, and the rest of the
file contains the ciphertext.

   The plaintext is encrypted in CBC mode.  The initial value for the
feedback is always set to a block filled with the letter 'A', and then
a block of random data is encrypted.  This garbage block will be
discarded on decryption.  Note that the random data is not generated in
a cryptographically secure way, and this may provide a tiny foothold for
an attacker.

   After the random block is generated, the magic string, length of the
original file, and original filename are all encrypted before the file
data is finally processed.  Some extra characters of padding may be
added to obtain an integer number of blocks.  This padding will also be
discarded on decryption.  Note that the plaintext file will be
completely read into memory before encryption is performed; no
buffering is done.  Therefore, don't encrypt 20-megabyte files unless
you're willing to face the consequences of a 20-megabyte process.

   Areas for improvements to `cipher' are: cryptographically secure
generation of random data for padding, key entry, and buffering of file
input.


File: pycrypt.info,  Node: Secure import,  Prev: cipher Demo,  Up: Demo Programs

Demo 2: `secimp' and `sign'
===========================

   `secimp' demonstrates an application of the Toolkit that may be
useful if Python is being used as an extension language for mail and Web
clients: secure importing of Python modules.  To use it, run `sign.py'
in a directory with several compiled Python files present.  It will use
the key in `testkey.py' to generate digital signatures for the compiled
Python code, and save both the signature and the code in a file ending
in `.pys'.  Then run `python -i secimp.py', and import a file by using
`secimport'.

   For example, if `foo.pys' was constructed, do `secimport('foo')'.
The import should succeed.  Now fire up Emacs or some other editor, and
change a string in the code in `foo.pys'; you might try changing a
letter in the name of a variable.  When you run `secimport('foo')', it
should raise an exception reporting the failed signature.  If you
execute the statement `__import__ = secimport', the secure import will
be used by default for all future module imports.  Alternatively, if
you were creating a restricted execution environment using `rexec.py',
you could place `secimport()' in the restricted environment's namespace
as the default import function.


File: pycrypt.info,  Node: Extending,  Next: Concept Index,  Prev: Demo Programs,  Up: Top

Extending the cryptography modules
**********************************

   Preserving the a common interface for cryptographic routines is a
good idea.  This chapter explains how to interface your own routines to
the Toolkit.

   The basic process is as follows:
  1. Modify the default definition of a C structure to include whatever
     instance data your algorithm requires.

  2. Write 3 or 4 standard routines.  Their names and parameters are
     specified in the following subsections.

  3. Modify `buildkit' to contain an entry for your new algorithm.
     Then run `buildkit' to rebuild all the source files.

  4. Send a copy of the code to me, if you like; code for new
     algorithms will be gratefully accepted.

* Menu:

* Creating a Custom Object::    Defining a C structure.
* Standard Routines::           What functions need to be written.
* Portability macros::          Macros to help writing portable modules.
* Informing the author::        Getting your code into the PCT.


File: pycrypt.info,  Node: Creating a Custom Object,  Next: Standard Routines,  Prev: Extending,  Up: Extending

Creating a Custom Object
========================

   In the C code for the interpreter, Python objects are defined as a
structure.  The default structure is the following:
     typedef struct
     {
      PCTObject_HEAD
     } ALGobject;

   `PCTObject_HEAD' is a preprocessor macro which will contain various
internal variables used by the interpreter; it must always be the first
item in the structure definition, and must not be followed by a
semicolon.  Following it, you can put whatever instance variables you
require.  Data that does not depend on the instance or key, such as a
static lookup table, need not be encapsulated inside objects; instead,
it can be defined as a variable interior to the module.

   As an example, for IDEA encryption, a schedule of encryption and
decryption data has to be maintained, resulting in the following
definition:
     typedef struct
     {
      PCTObject_HEAD
      int EK[6][9], DK[6][9];
     } IDEAobject;


File: pycrypt.info,  Node: Standard Routines,  Next: Portability macros,  Prev: Creating a Custom Object,  Up: Extending

Standard Routines
=================

   The interface to Python is implemented in the files ending in `.in',
so `hash.in' contains the basic code for modules containing hash
functions, for example.  `buildkit', a Python script, reads the
configuration file and generates source code by interweaving the
interface files and the implementation file.

   If your algorithm is called ALG, the implementation should be in the
file `ALG.c'. This is case-sensitive, as are the following function
names.

Hash functions
--------------

`void ALGinit(ALGobject *self);'
`void ALGupdate(ALGobject *self, char *buffer, int length);'
`PyObject *ALGdigest(ALGobject *self);'
`void ALGcopy(ALGobject *source, ALGobject *dest);'
 - Hashing function: void ALGinit (ALGobject *SELF)
     This function should initialize the hashing object, setting state
     variables to their expected initial state.

 - Hashing function: void ALGupdate (ALGobject *SELF,
     char *BUFFER, int LENGTH) This function should perform a hash on
     the region pointed to by BUFFER, which will contain LENGTH bytes.
     The contents of the object pointed to by SELF should be updated
     appropriately.

 - Hashing function: void ALGdigest (ALGobject *SELF)
     This function returns a string containing the value of the hash
     function.  The object should not be changed in any way by this
     function.  Some hash functions require some computation to be
     performed before returning a value; for example, the number of
     bytes may be hashed into the final value.  If this is the case for
     your hash function, you must make a copy of the object's data,
     perform the final computation on that copy, and return the result.

   Results are returned by calling a Python function,
`PyString_FromStringAndSize(char *STRING, int LENGTH)'.  This function
returns a string object which should be returned to the caller.  So,
the last line of the `ALGdigest' function might be:
       return PyString_FromStringAndSize(digest, 16);

 - Hashing function: void ALGcopy ALGobject *SOURCE, ALGobject *DEST)
     Given the source and destination objects, the state variables of
     the SOURCE object should be copied to the DEST object; the source
     object should not be altered in any way by the operation.

Block ciphers
-------------

`void ALGinit(ALGobject *SELF, unsigned char *KEY, int LENGTH);'
`PyObject *ALGencrypt(ALGobject *SELF, unsigned char *BLOCK);'
`PyObject *ALGdecrypt(ALGobject *SELF, unsigned char *BLOCK);'
 - Block encryption function: void ALGinit (ALGobject *SELF, unsigned
          char *KEY, int LENGTH)
     This function initializes a block cipher object to encrypt and
     decrypt with KEY.  If the cipher requires a fixed-length key, then
     the buffer pointed to by KEY will always of that length, and the
     value of LENGTH will be a random value that should be ignored.  If
     the algorithm accepts a variable-length key, then LENGTH will be
     nonzero, and will contain the size of the key.

 - Block encryption function: void ALGencrypt (ALGobject *SELF,
          unsigned char *BLOCK)
     This function should encrypt the data pointed to by BLOCK, using
     the key-dependent data contained in SELF.  Only ECB mode needs to
     be implemented; `block.in' takes care of the other ciphering modes.

 - Block encryption function: void ALGdecrypt (ALGobject *SELF,
          unsigned char *BLOCK)
     This function should decrypt the data pointed to by BLOCK, using
     the key-dependent data contained in SELF.


File: pycrypt.info,  Node: Portability macros,  Next: Informing the author,  Prev: Standard Routines,  Up: Extending

Portability macros
==================

   Implementation code must be carefully written to produce the same
results with any machine or compiler, without having to set any
compile-time definitions.  Code that is simply portable by nature is
preferable, but it is possible to detect features of the host machine
when new objects are created, and then execute special code to convert
data to a preferred form.

   While portability macros are written for speed, there's no need to
execute them on every encryption or updating operation.  Instead, add
variables to your object to hold the values of the portability macros,
and execute the macros only once per object, in your `ALGinit'
function.  Then the code can simply check the results of the macros and
act appropriately.

   Currently there is only one portability macro defined:

 - Macro: void TestEndianness (VARIABLE)
     Determines the endianness of the current machine, and sets
     VARIABLE to a constant representing the value for this machine.
     Possible constants are `PCT_BIG_ENDIAN' and `PCT_LITTLE_ENDIAN';
     they are defined along with the `TestEndianness' macro.


File: pycrypt.info,  Node: Informing the author,  Prev: Portability macros,  Up: Extending

Informing the author
====================

   Code for additional cryptographic algorithms can be mailed to me at
<akuchling@acm.org>.  You can make things much easier for me by doing
the following:
   * If you wrote the code, please release it into the public domain or
     under the MIT license .  If you didn't write it, please tell me
     where to find the original author or source code, so that I can
     check the licensing conditions.

   * Include some test data.  It is not sufficient to check that
     encryption and decryption cancel out properly.  An implementation
     might work fine on a single platform, but two machines with
     different endianness might produce different results.  This would
     be fatal for portability and interoperating programs.  So, please
     include test data; you can either send me patches to `test.py', or
     simply send me documents describing the data.


File: pycrypt.info,  Node: Concept Index,  Prev: Extending,  Up: Top

Concept Index
*************

* Menu:

* addEvent on RandomPool objects:        randpool module.
* ALGcopy:                               Standard Routines.
* ALGdecrypt:                            Standard Routines.
* ALGdigest:                             Standard Routines.
* ALGencrypt:                            Standard Routines.
* ALGinit:                               Standard Routines.
* ALGupdate:                             Standard Routines.
* ARC2 (block cipher):                   Encryption Algorithms.
* ARC4 (stream cipher) <1>:              Credits for Encryption Algorithms.
* ARC4 (stream cipher):                  Encryption Algorithms.
* bits:                                  randpool module.
* blocksize:                             Encryption Algorithms.
* Blowfish (block cipher) <1>:           Credits for Encryption Algorithms.
* Blowfish (block cipher):               Encryption Algorithms.
* Brown, Lawrence:                       Credits for Encryption Algorithms.
* buildkit:                              Standard Routines.
* bytes:                                 randpool module.
* C language:                            Design Goals.
* canencrypt on public-key objects:      Public Key Algorithms.
* cansign on public-key objects:         Public Key Algorithms.
* CAST (block cipher):                   Encryption Algorithms.
* cipher:                                cipher Demo.
* cipher (demo program):                 cipher Demo.
* construct:                             Public Key Algorithms.
* copy on hashing objects:               Hash Functions.
* crypt:                                 cipher Demo.
* Crypt Breaker's Workbench:             cipher Demo.
* Cyphers, Graven:                       Credits for Encryption Algorithms.
* decrypt on encryption objects:         Encryption Algorithms.
* decrypt on public-key objects:         Public Key Algorithms.
* DES (block cipher) <1>:                Credits for Encryption Algorithms.
* DES (block cipher):                    Encryption Algorithms.
* DES3 (block cipher):                   Encryption Algorithms.
* Diamond (block cipher):                Encryption Algorithms.
* digest on hashing objects:             Hash Functions.
* digestsize:                            Hash Functions.
* encrypt on encryption objects:         Encryption Algorithms.
* encrypt on public-key objects:         Public Key Algorithms.
* English2Key:                           RFC1751 module.
* Enigma:                                cipher Demo.
* entropy:                               randpool module.
* feedback mode, CBC <1>:                cipher Demo.
* feedback mode, CBC:                    Encryption Algorithms.
* feedback mode, CFB:                    Encryption Algorithms.
* feedback mode, ECB:                    Encryption Algorithms.
* generate:                              Public Key Algorithms.
* getBytes on RandomPool objects:        randpool module.
* Gutmann, Peter:                        Credits for Hash Functions.
* hasprivate on public-key objects:      Public Key Algorithms.
* HAVAL (hash function):                 Hash Functions.
* IDEA (block cipher) <1>:               Credits for Encryption Algorithms.
* IDEA (block cipher):                   Encryption Algorithms.
* Intel:                                 Design Goals.
* ITAR, regulations:                     Design Goals.
* IV:                                    Encryption Algorithms.
* Johnson, Michael Paul:                 Credits for Encryption Algorithms.
* Key2English:                           RFC1751 module.
* keysize:                               Encryption Algorithms.
* Kuchling, Andrew:                      Credits for Hash Functions.
* Kwan, Matthew:                         Credits for Encryption Algorithms.
* language, C:                           Design Goals.
* licensing terms:                       Design Goals.
* Linux:                                 cipher Demo.
* MD2 (hash function):                   Hash Functions.
* MD5 (hash function):                   Hash Functions.
* new:                                   Encryption Algorithms.
* Olson, Bryan:                          Credits for Encryption Algorithms.
* Outerbridge, Richard:                  Credits for Encryption Algorithms.
* Plumb, Colin:                          Credits for Hash Functions.
* publickey on public-key objects:       Public Key Algorithms.
* random numbers:                        randpool module.
* randomize on RandomPool objects:       randpool module.
* RandomPool:                            randpool module.
* RC4 (stream cipher):                   Encryption Algorithms.
* RC5 (block cipher):                    Encryption Algorithms.
* regulations, ITAR:                     Design Goals.
* RSA Data Security, Inc. <1>:           Encryption Algorithms.
* RSA Data Security, Inc.:               Hash Functions.
* Sapphire (stream cipher) <1>:          Credits for Encryption Algorithms.
* Sapphire (stream cipher):              Encryption Algorithms.
* save on RandomPool objects:            randpool module.
* Schneier, Bruce <1>:                   Credits for Encryption Algorithms.
* Schneier, Bruce:                       Acknowledgements.
* sci.crypt <1>:                         Credits for Encryption Algorithms.
* sci.crypt:                             Encryption Algorithms.
* SHA (hash function):                   Hash Functions.
* sign on public-key objects:            Public Key Algorithms.
* size on public-key objects:            Public Key Algorithms.
* stir on RandomPool objects:            randpool module.
* stream cipher:                         Encryption Algorithms.
* TestEndianness:                        Portability macros.
* Triple DES (block cipher):             Encryption Algorithms.
* update on hashing objects:             Hash Functions.
* verify on public-key objects:          Public Key Algorithms.
* Young, Eric:                           Credits for Encryption Algorithms.



Tag Table:
Node: Top101
Node: Introduction853
Node: Design Goals1016
Node: Acknowledgements4875
Node: Hash Functions5669
Node: Algorithm-specific Notes for Hash Functions9232
Node: Security Notes for Hash Functions9929
Node: Credits for Hash Functions12539
Node: Encryption Algorithms12855
Node: Algorithm-specific Notes for Encryption Algorithms19980
Node: Security Notes for Encryption Algorithms21119
Node: Credits for Encryption Algorithms22935
Node: Public Key Algorithms23907
Node: The ElGamal and DSA algorithms31607
Node: Security Notes for Public-key Algorithms33808
Node: Odds and Ends35120
Node: number module35579
Node: randpool module35732
Node: RFC1751 module43276
Node: Demo Programs44840
Node: cipher Demo45500
Node: Secure import48586
Node: Extending49899
Node: Creating a Custom Object50991
Node: Standard Routines52064
Node: Portability macros55727
Node: Informing the author56987
Node: Concept Index57995

End Tag Table
