KEYRING-SHA(2)

NAME

sha, md4, md5, sign, verify − cryptographic digests and digital signatures

SYNOPSIS

include "keyring.m";
keyring := load Keyring Keyring->PATH;
sha:fn(buf: array of byte, n: int, digest: array of byte,
state: ref DigestState): ref DigestState;
md4:fn(buf: array of byte, n: int, digest: array of byte,
state: ref DigestState): ref DigestState;
md5:fn(buf: array of byte, n: int, digest: array of byte,
state: ref DigestState): ref DigestState;
sign:fn(sk: ref SK, exp: int, state: ref DigestState,
ha: string): ref Certificate;
verify:fn(pk: ref PK, cert: ref Certificate,
state: ref DigestState): int;

DESCRIPTION

Sha, md4 and md5 are cryptographically secure hash functions that produce output called a message digest. Each function computes a hash of n bytes of the data in buf, and updates the current state. They can be called iteratively to form a single digest for many data blocks. The state is kept in the DigestState value referenced by state between calls. State should be nil on the first call, and a newly allocated DigestState will be returned for use in subsequent calls. On a call in which digest is not nil, the hash is completed and copied into the digest array. Sha produces a 20-byte hash (SHAdlen), md4 and md5 a 16-byte one (MD4len and MD5len).

Sign creates a digital signature of a digest from the concatenation of: a message, the name of the signer, and an expiration time. State is the digest state after running sha, md4 or md5 over the message. Ha is a string specifying the hash algorithm to use: "sha", "md4" or "md5". Sign extends the digest to cover the signer’s name (taken from the private key, sk) and the expiration time. It returns a certificate containing the digital signature of the digest, signer name, hash algorithm and signature algorithm. If any parameter is invalid, sign returns nil. The signature algorithm is implied by the type of the private key.

Verify uses public key pk to verify a certificate. It returns non-zero (true) if the certificate is valid; zero (false) otherwise. State is the digest state after running the chosen digest algorithm over the message.

EXAMPLES

A program to read a file and hash it using SHA might contain the following inner loop:

state: ref DigestState = nil;
while((n := sys->read(fd, buf, len buf)) > 0)
state = kr->sha(buf, n, nil, state);
digest := array[kr->SHAdlen] of byte;
kr->sha(buf, 0, digest, state);

SOURCE

/interp/keyring.c
/crypt/md4.c
/crypt/md5.c
/crypt/sha.c