source: vbox/trunk/src/libs/openssl-1.1.1h/doc/man3/SHA256_Init.pod@ 86719

=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.

=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 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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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