ref: 75c92428225428c8fde2d015f010e608a0b12f1d
dir: purgatorio/man/2/crypt-crypt
.TH CRYPT-CRYPT 2
.SH NAME
crypt: aessetup, aescbc, dessetup, descbc, desecb, ideasetup, ideacbc, ideaecb \- data encryption
.SH SYNOPSIS
.EX
include "ipints.m";
include "crypt.m";
crypt := load Crypt Crypt->PATH;
Encrypt: con 0;
Decrypt: con 1;
AESbsize: con 16;
aessetup: fn(key: array of byte, ivec: array of byte): ref AESstate;
aescbc: fn(state: ref AESstate, buf: array of byte,
n: int, direction: int);
BFbsize: con 8;
blowfishsetup: fn(key: array of byte, ivec: array of byte): ref BFstate;
blowfishcbc: fn(state: ref BFstate, buf: array of byte,
n: int, direction: int);
DESbsize: con 8;
dessetup: fn(key: array of byte, ivec: array of byte): ref DESstate;
descbc: fn(state: ref DESstate, buf: array of byte,
n: int, direction: int);
desecb: fn(state: ref DESstate, buf: array of byte,
n: int, direction: int);
IDEAbsize: con 8;
ideasetup: fn(key: array of byte, ivec: array of byte): ref IDEAstate;
ideacbc: fn(state: ref IDEAstate, buf: array of byte,
n: int, direction: int);
ideaecb: fn(state: ref IDEAstate, buf: array of byte,
n: int, direction: int);
.EE
.SH DESCRIPTION
These functions encrypt and decrypt blocks of data using different
encryption algorithms.
The interfaces are similar.
.PP
Each algorithm has an adt that holds the current state for a given encryption.
It is produced by the setup function for the algorithm,
.IB alg setup ,
which is given a secret
.I key
and an initialisation vector
.IR ivec .
A sequence of blocks of data can then be encrypted or decrypted by repeatedly calling
.IB alg cbc
(for `cipher block chaining'), or
.IB alg ebc
(the less secure `electronic code book', if provided).
On each call,
.I buf
provides
.I n
bytes of the data to encrypt or decrypt.
.I N
must be a multiple of the encryption block size
.IB ALG bsize .
Exceptionally,
.B aescbc
allows
.I n
to be other than a multiple of
.B AESbsize
in length, but then
for successful decryption, the decryptor must use the same
sequence of buffer sizes as the encryptor.
.I Direction
is the constant
.B Encrypt
or
.B Decrypt
as required.
.I State
maintains the encryption state, initially produced by the setup function,
and updated as each buffer is encrypted or decrypted.
.PP
The algorithms currently available are:
.TP
.B aes
The Advanced Encryption Standard, AES (also known as Rijndael).
The
.I key
should be 16, 24 or 32 bytes long (128, 192 or 256 bits).
.I Ivec
should be
.B AESbsize
bytes of random data: random enough to be unlikely to be reused but
not cryptographically strongly unpredictable.
.TP
.B blowfish
Bruce Schneier's symmetric block cipher.
The
.I key
is any length from 4 to 56 bytes.
.I Ivec
if non-nil is
.B BFbsize
bytes of random data.
For
.BR blowfishcbc ,
.I n
must be a multiple of
.BR BFbsize .
.TP
.B des
The older Data Encryption Standard, DES.
.I Key
is 8 bytes (64 bits), containing a 56-bit key
encoded into 64 bits where every eighth bit is parity.
.I Ivec
is
.B DESbsize
bytes of random data.
.TP
.B idea
The International Data Encryption Standard, IDEA™.
The
.I key
is 16 bytes long (128 bits).
.I Ivec
is
.B IDEAbsize
bytes of random data.
.SH SEE ALSO
.IR crypt-intro (2),
.IR crypt-rc4 (2),
.IR security-random (2)
.PP
IDEA was patented by Ascom-Tech AG (EP 0 482 154 B1, US005214703),
currently held by iT_SEC Systec Ltd.
The patent expired in 2012.