Cross-linked the man(1) pages of kdf & pkeyutl.

[thirdparty/openssl.git] / doc / man3 / SHA256_Init.pod

=pod

=head1 NAME

SHA1, SHA1_Init, SHA1_Update, SHA1_Final, SHA224, SHA224_Init, SHA224_Update,
SHA224_Final, SHA256, SHA256_Init, SHA256_Update, SHA256_Final, SHA384,
SHA384_Init, SHA384_Update, SHA384_Final, SHA512, SHA512_Init, SHA512_Update,
SHA512_Final - Secure Hash Algorithm

=head1 SYNOPSIS

 #include <openssl/sha.h>

 int SHA1_Init(SHA_CTX *c);
 int SHA1_Update(SHA_CTX *c, const void *data, size_t len);
 int SHA1_Final(unsigned char *md, SHA_CTX *c);
 unsigned char *SHA1(const unsigned char *d, size_t n,
                     unsigned char *md);

 int SHA224_Init(SHA256_CTX *c);
 int SHA224_Update(SHA256_CTX *c, const void *data, size_t len);
 int SHA224_Final(unsigned char *md, SHA256_CTX *c);
 unsigned char *SHA224(const unsigned char *d, size_t n,
                       unsigned char *md);

 int SHA256_Init(SHA256_CTX *c);
 int SHA256_Update(SHA256_CTX *c, const void *data, size_t len);
 int SHA256_Final(unsigned char *md, SHA256_CTX *c);
 unsigned char *SHA256(const unsigned char *d, size_t n,
                       unsigned char *md);

 int SHA384_Init(SHA512_CTX *c);
 int SHA384_Update(SHA512_CTX *c, const void *data, size_t len);
 int SHA384_Final(unsigned char *md, SHA512_CTX *c);
 unsigned char *SHA384(const unsigned char *d, size_t n,
                       unsigned char *md);

 int SHA512_Init(SHA512_CTX *c);
 int SHA512_Update(SHA512_CTX *c, const void *data, size_t len);
 int SHA512_Final(unsigned char *md, SHA512_CTX *c);
 unsigned char *SHA512(const unsigned char *d, size_t n,
                       unsigned char *md);

=head1 DESCRIPTION

Applications should use the higher level functions
L<EVP_DigestInit(3)> etc. instead of calling the hash
functions directly.

SHA-1 (Secure Hash Algorithm) is a cryptographic hash function with a
160 bit output.

SHA1() computes the SHA-1 message digest of the B<n>
bytes at B<d> and places it in B<md> (which must have space for
SHA_DIGEST_LENGTH == 20 bytes of output). If B<md> is NULL, the digest
is placed in a static array. Note: setting B<md> to NULL is B<not thread safe>.

The following functions may be used if the message is not completely
stored in memory:

SHA1_Init() initializes a B<SHA_CTX> structure.

SHA1_Update() can be called repeatedly with chunks of the message to
be hashed (B<len> bytes at B<data>).

SHA1_Final() places the message digest in B<md>, which must have space
for SHA_DIGEST_LENGTH == 20 bytes of output, and erases the B<SHA_CTX>.

The SHA224, SHA256, SHA384 and SHA512 families of functions operate in the
same way as for the SHA1 functions. Note that SHA224 and SHA256 use a
B<SHA256_CTX> object instead of B<SHA_CTX>. SHA384 and SHA512 use B<SHA512_CTX>.
The buffer B<md> must have space for the output from the SHA variant being used
(defined by SHA224_DIGEST_LENGTH, SHA256_DIGEST_LENGTH, SHA384_DIGEST_LENGTH and
SHA512_DIGEST_LENGTH). Also note that, as for the SHA1() function above, the
SHA224(), SHA256(), SHA384() and SHA512() functions are not thread safe if
B<md> is NULL.

The predecessor of SHA-1, SHA, is also implemented, but it should be
used only when backward compatibility is required.

=head1 RETURN VALUES

SHA1(), SHA224(), SHA256(), SHA384() and SHA512() return a pointer to the hash
value.

SHA1_Init(), SHA1_Update() and SHA1_Final() and equivalent SHA224, SHA256,
SHA384 and SHA512 functions return 1 for success, 0 otherwise.

=head1 CONFORMING TO

US Federal Information Processing Standard FIPS PUB 180-4 (Secure Hash
Standard),
ANSI X9.30

=head1 SEE ALSO

L<EVP_DigestInit(3)>

=head1 COPYRIGHT

Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

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