MD5(3) | Library Functions Manual | MD5(3)

# NAME

`MD4`, `MD5`, `MD4_Init`, `MD4_Update`, `MD4_Final`, `MD5_Init`, `MD5_Update`, `MD5_Final` — MD4 and MD5 hash functions

# SYNOPSIS

library “libcrypto”
`#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);

# DESCRIPTION

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

`MD4`() and `MD5`() compute the MD4 and MD5 message digest of the n bytes at d and place it in md, which must have space for `MD4_DIGEST_LENGTH` == `MD5_DIGEST_LENGTH` == 16 bytes of output.

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

`MD5_Init`() initializes a MD5_CTX structure.

`MD5_Update`() can be called repeatedly with chunks of the message to be hashed (len bytes at data).

`MD5_Final`() places the message digest in md, which must have space for `MD5_DIGEST_LENGTH` == 16 bytes of output, and erases the MD5_CTX.

`MD4_Init`(), `MD4_Update`(), and `MD4_Final`() are analogous using an MD4_CTX structure.

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

# RETURN VALUES

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

`MD4_Init`(), `MD4_Update`(), `MD4_Final`(), `MD5_Init`(), `MD5_Update`(), and `MD5_Final`() return 1 for success or 0 otherwise.

# SEE ALSO

EVP_DigestInit(3)

# STANDARDS

RFC 1320, RFC 1321

# HISTORY

`MD5`(), `MD5_Init`(), `MD5_Update`(), and `MD5_Final`() appeared in SSLeay 0.4 or earlier and have been available since OpenBSD 2.4.

`MD4`(), `MD4_Init`(), `MD4_Update`(), and `MD4_Final`() first appeared in OpenSSL 0.9.6 and have been available since OpenBSD 2.9.

# CAVEATS

Other implementations allow md in `MD4`() and `MD5`() to be `NULL` and return a static array, which is not thread safe.

June 8, 2025 | Debian