MD4Init, MD4Update, MD4Pad, MD4Final, MD4End, MD4File, MD4FileChunk, MD4Data - calculate the RSA Data Security, Inc., ‘‘MD4’’ message digest

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.Lb libmd

.In sys/types.h
.In md4.h void MD4Init MD4_CTX *context void MD4Update MD4_CTX *context const unsigned char *data unsigned int len void MD4Pad MD4_CTX *context void MD4Final unsigned char digest[16] MD4_CTX *context char * MD4End MD4_CTX *context char *buf char * MD4File const char *filename char *buf char * MD4FileChunk const char *filename char *buf off_t offset off_t length char * MD4Data const unsigned char *data unsigned int len char *buf

The MD4 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 does not disclose the actual input.

MD2 is the slowest, MD4 is the fastest and MD5 is somewhere in the middle. MD2 can only be used for Privacy-Enhanced Mail. MD4 has now been broken; it should only be used where necessary for backward compatibility. MD5 has not yet (1999-02-11) been broken, but sufficient attacks have been made that its security is in some doubt. The attacks on both MD4 and MD5 are both in the nature of finding "collisions" [en] 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.

The MD4Init, MD4Update, and MD4Final functions are the core functions. Allocate an
.Vt MD4_CTX , initialize it with MD4Init, run over the data with MD4Update, and finally extract the result using MD4Final.

The MD4Pad function can be used to pad message data in same way as done by MD4Final without terminating calculation.

The MD4End function is a wrapper for MD4Final which converts the return value to a 33-character (including the terminating ’\0’) ASCII string which represents the 128 bits in hexadecimal.

The MD4File function calculates the digest of a file, and uses MD4End to return the result. If the file cannot be opened, a null pointer is returned. The MD4FileChunk function is similar to MD4File, but it only calculates the digest over a byte-range of the file specified, starting at offset and spanning length bytes. If the length parameter is specified as 0, or more than the length of the remaining part of the file, MD4FileChunk calculates the digest from offset to the end of file. The MD4Data function calculates the digest of a chunk of data in memory, and uses MD4End to return the result.

When using MD4End, MD4File, or MD4Data, 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 33 characters of buffer space.

md2(3), md4(3), md5(3), sha(3)
.Rs The MD2 Message-Digest Algorithm
.Re
.Rs The MD4 Message-Digest Algorithm
.Re
.Rs The MD5 Message-Digest Algorithm
.Re
.Rs Frequently Asked Questions About today’s Cryptography
.Re
.Rs Alf Swindles Ann
.Re
.Rs On Recent Results for MD2, MD4 and MD5
.Re

These functions appeared in
.Fx 2.0 .

The original MD4 routines were developed by RSA Data Security, Inc., and published in the above references. This code is derived directly from these implementations by
.An Poul-Henning Kamp Aq phk@FreeBSD.org

Phk ristede runen.

No method is known to exist which finds two files having the same hash value, nor to find a file with a specific hash value. There is on the other hand no guarantee that such a method does not exist.

MD2 has only been licensed for use in Privacy Enhanced Mail. Use MD4 or MD5 if that is not what you are doing. Copyright (C) 1991-2, RSA Data Security, Inc. Created 1991. All rights reserved.

License to copy and use this software is granted provided that it is identified as the "RSA Data Security, Inc. MD4 Message-Digest Algorithm" in all material mentioning or referencing this software or this function. License is also granted to make and use derivative works provided that such works are identified as "derived from the RSA Data Security, Inc. MD4 Message-Digest Algorithm" in all material mentioning or referencing the derived work.

RSA Data Security, Inc. makes no representations concerning either the merchantability of this software or the suitability of this software for any particular purpose. It is provided "as is" without express or implied warranty of any kind.

These notices must be retained in any copies of any part of this documentation and/or software.

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