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NAME

SYNOPSIS

#include <librock/target/types.c>
#include <librock/data.h>

void
librock_MD5Init (librock_MD5_CTX *ctx);

void
librock_MD5Update (librock_MD5_CTX *ctx,
                   unsigned char *buf,
                   unsigned int len);

void
librock_MD5Final (unsigned char result[16], /* result stored there */
                  librock_MD5_CTX *ctx);

DESCRIPTION

To compute the MD5 Message-Digest, declare a librock_MD5_CTX (a typedef'ed structure) which is initialized with a call to librock_MD5Init(). After making one or more calls to librock_MD5Update(), call librock_MD5Final() to place the result into a 16 byte buffer.

The algorithm is described in IETF RFC1321 (R. Rivest. RFC 1321: The MD5 Message-Digest Algorithm. April 1992.) The design property that is that the 16 byte result is unique for unique input, and it is computationally infeasible to create text with a given result. That RFC also has this implementation source code.

MD5 message digests are used as a unique "fingerprint" (which can verify the integrity of a file or character sequence without a byte by byte comparison.) They are also used as unique hash values. (The computational load to compute the md5 result is significant compared to CRC32, so it should be used only when the uniqueness of the result for unique input is essential, or protecting against generated input which matches a known result is required.)

librock_MD5Update() may save not more than 64 bytes of a buffer in the librock_MD5_CTX structure in between calls. That memory is zeroed on librock_MD5Final. But callers may want to use care when working with input which must not be exposed.

Typical use:

#ifdef librock_TYPICAL_USE_MD5Update
    #include <librock/target/types.c>
    #include <librock/data.h>
    #include <stdio.h>
    unsigned char digest[16];
    char ascdigest[16*2+1];
    char buf[8192];
    int ind;
    librock_MD5_CTX md5Ctx;
    FILE * f = 0;

    librock_MD5Init(&md5Ctx);

    if (f) {
        while(!feof(f)) {
            int cnt = fread(buf,1,sizeof(buf),f);
            if (cnt <= 0) {
                break;
            }
            librock_MD5Update(&md5Ctx,(unsigned char *) buf,cnt);
        }
    } else {
        librock_MD5Update(&md5Ctx,"Hello!",6);
    }
    librock_MD5Final(digest,&md5Ctx);
    /* Now create ASCII hexadecimal representation */
    ascdigest[0] = '\0';
    ind = 0;
    while(ind < 16) {
        sprintf(ascdigest+strlen(ascdigest),"%02x",digest[ind] & 0xff);
        ind++;
    }
    printf("%s\n",ascdigest);
#endif

USES

  // No external calls
  // Well-behaved in multi-threaded uses.

LICENSE

  Copyright (C) 1991-2, RSA Data Security, Inc. Created 1991. All
  rights reserved.
  Licensed under BSD-ish license, NO WARRANTY. Copies must retain this block.
  License text in <librock/license/md5rsa.txt> librock_LIDESC_HC=ec1a2c9549fec7790a691ac943b38f06

Source Code

This software is part of Librock

• Source code which is Open-source, Free (Libre) and free (no cost)
• Namespace limited. All compile-time macros and names visible at link time are prefixed by "librock_". Integrate into your project and expect no name collisions.
• Stable API means new functions get new names so that there is no risk that updating a source file will break existing applications.
• Highly portable, cross-platform, and multithread compatible. Works with many machines, compilers, and operating systems (gcc/MSVC/Windows/Linux/BSD).

Verbatim copying and distribution of this generated page is permitted in any medium provided that no changes are made.
(The source of this manual page may be covered by a more permissive license which allows modifications.)

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