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=head1 NAME

MD2, MD4, MD5, MD2_Init, MD2_Update, MD2_Final, MD4_Init, MD4_Update,
MD4_Final, MD5_Init, MD5_Update, MD5_Final - MD2, MD4, and MD5 hash functions

=head1 SYNOPSIS

 #include <openssl/md2.h>

 unsigned char *MD2(const unsigned char *d, unsigned long n,
                  unsigned char *md);

 int MD2_Init(MD2_CTX *c);
 int MD2_Update(MD2_CTX *c, const unsigned char *data,
                  unsigned long len);
 int MD2_Final(unsigned char *md, MD2_CTX *c);


 #include <openssl/md4.h>

 unsigned char *MD4(const unsigned char *d, unsigned long n,
                  unsigned char *md);

 int MD4_Init(MD4_CTX *c);
 int MD4_Update(MD4_CTX *c, const void *data,
                  unsigned long len);
 int MD4_Final(unsigned char *md, MD4_CTX *c);


 #include <openssl/md5.h>

 unsigned char *MD5(const unsigned char *d, unsigned long n,
                  unsigned char *md);

 int MD5_Init(MD5_CTX *c);
 int MD5_Update(MD5_CTX *c, const void *data,
                  unsigned long len);
 int MD5_Final(unsigned char *md, MD5_CTX *c);

=head1 DESCRIPTION

MD2, MD4, and MD5 are cryptographic hash functions with a 128 bit output.

MD2(), MD4(), and MD5() compute the MD2, MD4, and MD5 message digest
of the B<n> bytes at B<d> and place it in B<md> (which must have space
for MD2_DIGEST_LENGTH == MD4_DIGEST_LENGTH == MD5_DIGEST_LENGTH == 16
bytes of output). If B<md> is NULL, the digest is placed in a static
array.

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

MD2_Init() initializes a B<MD2_CTX> structure.

MD2_Update() can be called repeatedly with chunks of the message to
be hashed (B<len> bytes at B<data>).

MD2_Final() places the message digest in B<md>, which must have space
for MD2_DIGEST_LENGTH == 16 bytes of output, and erases the B<MD2_CTX>.

MD4_Init(), MD4_Update(), MD4_Final(), MD5_Init(), MD5_Update(), and
MD5_Final() are analogous using an B<MD4_CTX> and B<MD5_CTX> structure.

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

=head1 NOTE

MD2, MD4, and MD5 are recommended only for compatibility with existing
applications. In new applications, SHA-1 or RIPEMD-160 should be
preferred.

=head1 RETURN VALUES

MD2(), MD4(), and MD5() return pointers to the hash value. 

MD2_Init(), MD2_Update(), MD2_Final(), MD4_Init(), MD4_Update(),
MD4_Final(), MD5_Init(), MD5_Update(), and MD5_Final() return 1 for
success, 0 otherwise.

=head1 CONFORMING TO

RFC 1319, RFC 1320, RFC 1321

=head1 SEE ALSO

L<sha(3)|sha(3)>, L<ripemd(3)|ripemd(3)>, L<EVP_DigestInit(3)|EVP_DigestInit(3)>

=head1 HISTORY

MD2(), MD2_Init(), MD2_Update() MD2_Final(), MD5(), MD5_Init(),
MD5_Update() and MD5_Final() are available in all versions of SSLeay
and OpenSSL.

MD4(), MD4_Init(), and MD4_Update() are available in OpenSSL 0.9.6 and
above.

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