include "keyring.m";
keyring := load Keyring Keyring->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);

Each algorithm has an adt that holds the current state for a given encryption. It is produced by the setup function for the algorithm, algsetup, which is given a secret key and an initialisation vector ivec. A sequence of blocks of data can then be encrypted or decrypted by repeatedly calling algcbc (for `cipher block chaining'), or algebc (the less secure `electronic code book', if provided). On each call, buf provides n bytes of the data to encrypt or decrypt. N must be a multiple of the encryption block size ALGbsize. Exceptionally, aescbc allows n to be other than a multiple of AESbsize in length, but then for successful decryption, the decryptor must use the same sequence of buffer sizes as the encryptor. Direction is the constant Encrypt or Decrypt as required. State maintains the encryption state, initially produced by the setup function, and updated as each buffer is encrypted or decrypted.

The algorithms currently available are:

aes

The Advanced Encryption Standard, AES (also known as Rijndael). The key should be 16, 24 or 32 bytes long (128, 192 or 256 bits). Ivec should be AESbsize bytes of random data: random enough to be unlikely to be reused but not cryptographically strongly unpredictable.

blowfish

Bruce Schneier's symmetric block cipher. The key is any length from 4 to 56 bytes. Ivec if non-nil is BFbsize bytes of random data. For blowfishcbc, n must be a multiple of BFbsize.

des

The older Data Encryption Standard, DES. Key is 8 bytes (64 bits), containing a 56-bit key encoded into 64 bits where every eighth bit is parity. Ivec is DESbsize bytes of random data.

idea

The International Data Encryption Standard, IDEA™. The key is 16 bytes long (128 bits). Ivec is IDEAbsize bytes of random data.

IDEA was patented by Ascom-Tech AG (EP 0 482 154 B1, US005214703), currently held by iT_SEC Systec Ltd. At time of writing, there was no licence fee required for noncommercial use but check the current licensing policy of iT_SEC Systec Ltd, especially for commercial use.