NAME
md4, md5, sha1, sha2_224, sha2_256, sha2_384, sha2_512, aes, hmac_x, hmac_md5, hmac_sha1, hmac_sha2_224, hmac_sha2_256, hmac_sha2_384, hmac_sha2_512, hmac_aes, md5pickle, md5unpickle, sha1pickle, sha1unpickle – cryptographically secure hashes

SYNOPSIS
#include <u.h>
#include <libc.h>
#include <mp.h>
#include <libsec.h>
#define DS DigestState /* only to abbreviate SYNOPSIS */

DS* md4(uchar *data, ulong dlen, uchar *digest, DS *state)

DS* md5(uchar *data, ulong dlen, uchar *digest, DS *state)

char*        md5pickle(MD5state *state)

MD5state*    md5unpickle(char *p);

DS* sha1(uchar *data, ulong dlen, uchar *digest, DS *state)

char*        sha1pickle(SHA1state *state)

SHA1state* sha1unpickle(char *p);

DS* sha2_224(uchar *data, ulong dlen, uchar *digest, DS *state)

DS* sha2_256(uchar *data, ulong dlen, uchar *digest, DS *state)

DS* sha2_384(uchar *data, ulong dlen, uchar *digest, DS *state)

DS* sha2_512(uchar *data, ulong dlen, uchar *digest, DS *state)

DS* aes(uchar *data, ulong dlen, uchar *digest, DS *state)

DS* hmac_x(uchar *p, ulong len, uchar *key, ulong klen, uchar *digest, DS *s, DS*(*x)(uchar*, ulong, uchar*, DS*), int xlen)

DS* hmac_md5(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DS *state)

DS* hmac_sha1(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DS *state)

DS* hmac_sha2_224(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DS *state)

DS* hmac_sha2_256(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DS *state)

DS* hmac_sha2_384(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DS *state)

DS* hmac_sha2_512(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DS *state)

DS* hmac_aes(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DS *state)

DESCRIPTION
We support several secure hash functions. The output of a hash is called a digest. A hash is secure if, given the hashed data and the digest, it is difficult to predict the change to the digest resulting from some change to the data without rehashing the whole data. Therefore, if a secret is part of the hashed data, the digest can be used as an integrity check of the data by anyone possessing the secret.

The routines md4, md5, sha1, sha2_224, sha2_256, sha2_384, sha2_512, aes, hmac_md5, hmac_sha1, hmac_sha2_224, hmac_sha2_256, hmac_sha2_384, hmac_sha2_512, and hmac_aes differ only in the length of the resulting digest and in the security of the hash. Sha2_* and hmac_sha2_* are the SHA–2 functions; the number after the final underscore is the number of bits in the resulting digest. Usage for each is the same. The first call to the routine should have nil as the state parameter. This call returns a state which can be used to chain subsequent calls. The last call should have digest non–nil. Digest must point to a buffer of at least the size of the digest produced. This last call will free the state and copy the result into digest.

The constants MD4dlen, MD5dlen, SHA1dlen, SHA2_224dlen, SHA2_256dlen, SHA2_384dlen, SHA2_512dlen, and AESdlen define the lengths of the digests.

Hmac_md5, hmac_sha1, hmac_sha2_224, hmac_sha2_256, hmac_sha2_384, hmac_sha2_512, and hmac_aes are used slightly differently. These hash algorithms are keyed and require a key to be specified on every call. The digest lengths for these hashes are the obvious ones from the above list of length constants. These routines all call hmac_x internally, but hmac_x is not intended for general use.

The functions md5pickle and sha1pickle marshal the state of a digest for transmission. Md5unpickle and sha1unpickle unmarshal a pickled digest. All four routines return a pointer to a newly malloc(2)'d object.

EXAMPLES
To hash a single buffer using md5:
uchar digest[MD5dlen];
md5(data, len, digest, nil);

To chain a number of buffers together, bounded on each end by some secret:
char buf[256];
uchar digest[MD5dlen];
DigestState *s;
s = md5("my password", 11, nil, nil);
while((n = read(fd, buf, 256)) > 0)
md5(buf, n, nil, s);
md5("drowssap ym", 11, digest, s);

SOURCE
/sys/src/libsec

SEE ALSO
aes(2), blowfish(2), des(2), elgamal(2), rc4(2), rsa(2)
/lib/rfc/rfc2104   HMAC specification
Copyright © 2017 Alcatel-Lucent. All rights reserved.