|MD5INIT(3)||Library Functions Manual||MD5INIT(3)|
— calculate MD5 message digest
*context, const u_int8_t
char *filename, char
char *filename, char
*buf, off_t offset,
u_int8_t *data, size_t
The MD5 functions calculate a 128-bit cryptographic checksum (digest) for any number of input bytes. A cryptographic checksum is a one-way hash-function, that is, you cannot find (except by exhaustive search) the input corresponding to a particular output. This net result is a “fingerprint” of the input-data, which doesn't disclose the actual input.
MD5 has been broken; it should only be used where necessary for backward compatibility. The attack on MD5 is in the nature of finding “collisions” — that is, multiple inputs which hash to the same value. It is still unlikely for an attacker to be able to determine the exact original input given a hash value.
functions are the core functions. Allocate an MD5_CTX,
initialize it with
MD5Init(), run over the data with
MD5Update(), and finally extract the result using
MD5Pad() function can be used to apply
padding to the message digest as in
the current context can still be used with
MD5Transform() function is used by
MD5Update() to hash 512-bit blocks and forms the
core of the algorithm. Most programs should use the interface provided by
MD5Final() instead of calling
MD5End() is a wrapper for
MD5Final() which converts the return value to an
MD5_DIGEST_STRING_LENGTH-character (including the terminating '\0') ASCII
string which represents the 128 bits in hexadecimal.
MD5File() calculates the digest of a file,
MD5End() to return the result. If the file
cannot be opened, a null pointer is returned.
MD5FileChunk() behaves like
MD5File() but calculates the digest only for that
portion of the file starting at offset and continuing
for length bytes or until end of file is reached,
whichever comes first. A zero length can be specified
to read until end of file. A negative length or
offset will be ignored.
MD5Data() calculates the digest of a chunk of data
in memory, and uses
MD5End() to return the
MD5Data(), the buf argument
can be a null pointer, in which case the returned string is allocated with
malloc(3) and subsequently must be
explicitly deallocated using free(3) after
use. If the buf argument is non-null it must point to
at least MD5_DIGEST_STRING_LENGTH characters of buffer space.
H. Dobbertin, Alf Swindles Ann, CryptoBytes, 1(3):5, 1995.
MJ. B. Robshaw, On Recent Results for MD4 and MD5, RSA Laboratories Bulletin, 4, November 12, 1996.
Hans Dobbertin, Cryptanalysis of MD5 Compress.
R. Rivest, The MD5 Message Digest Algorithm, RFC 1321, April 1992.
These functions appeared in OpenBSD 2.0.
The original MD5 routines were developed by RSA Data Security, Inc., and published in the above references. This code is derived from a public domain implementation written by Colin Plumb.
MD5Data() helper functions are derived from code
written by Poul-Henning Kamp.
Collisions have been found for the full version of MD5. The use of the SHA2 functions is recommended instead.
|August 30, 2019||OpenBSD-current|