'\" te
.\"  Copyright (c) 2007, Sun Microsystems, Inc.  All Rights Reserved
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.TH MD5 3EXT "Nov 13, 2007"
.SH NAME
md5, md5_calc, MD5Init, MD5Update, MD5Final \- MD5 digest functions
.SH SYNOPSIS
.LP
.nf
\fBcc\fR [ \fIflag\fR ... ] \fIfile\fR ... \fB-lmd5\fR [ \fIlibrary\fR ... ]
#include <md5.h>

\fBvoid\fR \fBmd5_calc\fR(\fBunsigned char *\fR\fIoutput\fR, \fBunsigned char *\fR\fIinput\fR,
     \fBunsigned int\fR \fIinlen\fR);
.fi

.LP
.nf
\fBvoid\fR \fBMD5Init\fR(\fBMD5_CTX *\fR\fIcontext\fR);
.fi

.LP
.nf
\fBvoid\fR \fBMD5Update\fR(\fBMD5_CTX *\fR\fIcontext\fR, \fBunsigned char *\fR\fIinput\fR,
     \fBunsigned int\fR \fIinlen\fR);
.fi

.LP
.nf
\fBvoid\fR \fBMD5Final\fR(\fBunsigned char *\fR\fIoutput\fR, \fBMD5_CTX *\fR\fIcontext\fR);
.fi

.SH DESCRIPTION
.sp
.LP
These functions implement the MD5 message-digest algorithm, which takes as
input a message of arbitrary length and produces as output a 128-bit
"fingerprint" or "message digest" of the input. It is intended for digital
signature applications, where large file must be "compressed" in a secure
manner before being encrypted with a private (secret) key under a public-key
cryptosystem such as RSA.
.SS "\fBmd5_calc()\fR"
.sp
.LP
The \fBmd5_calc()\fR function computes an MD5 digest on a single message block.
The \fIinlen\fR-byte block is pointed to by \fIinput\fR, and the 16-byte MD5
digest is written to \fIoutput\fR.
.SS "\fBMD5Init()\fR, \fBMD5Update()\fR, \fBMD5Final()\fR"
.sp
.LP
The \fBMD5Init()\fR, \fBMD5Update()\fR, and \fBMD5Final()\fR functions allow an
MD5 digest to be computed over multiple message blocks; between blocks, the
state of the MD5 computation is held in an MD5 context structure, allocated by
the caller. A complete digest computation consists of one call to
\fBMD5Init()\fR, one or more calls to \fBMD5Update()\fR, and one call to
\fBMD5Final()\fR, in that order.
.sp
.LP
The \fBMD5Init()\fR function initializes the MD5 context structure pointed to
by \fIcontext\fR.
.sp
.LP
The \fBMD5Update()\fR function computes a partial MD5 digest on the
\fIinlen\fR-byte message block pointed to by \fIinput\fR, and updates the MD5
context structure pointed to by \fIcontext\fR accordingly.
.sp
.LP
The \fBMD5Final()\fR function generates the final MD5 digest, using the MD5
context structure pointed to by \fIcontext\fR; the 16-byte MD5 digest is
written to \fIoutput\fR. After calling \fBMD5Final()\fR, the state of the
context structure is undefined; it must be reinitialized with \fBMD5Init()\fR
before being used again.
.SH RETURN VALUES
.sp
.LP
These functions do not return a value.
.SH EXAMPLES
.LP
\fBExample 1 \fRAuthenticate a message found in multiple buffers
.sp
.LP
The following is a sample function that must authenticate a message that is
found in multiple buffers. The calling function provides an authentication
buffer that will contain the result of the MD5 digest.

.sp
.in +2
.nf
#include <sys/types.h>
#include <sys/uio.h>
#include <md5.h>

int
AuthenticateMsg(unsigned char *auth_buffer, struct iovec
                *messageIov, unsigned int num_buffers)
{
    MD5_CTX md5_context;
    unsigned int i;

    MD5Init(&md5_context);

    for(i=0; i<num_buffers; i++)
    {
         MD5Update(&md5_context, messageIov->iov_base,
                   messageIov->iov_len);
         messageIov += sizeof(struct iovec);
    }

    MD5Final(auth_buffer, &md5_context);

    return 0;
}
.fi
.in -2

.LP
\fBExample 2 \fRUse \fBmd5_calc()\fR to generate the MD5 digest
.sp
.LP
Since the buffer to be computed is contiguous, the \fBmd5_calc()\fR function
can be used to generate the MD5 digest.

.sp
.in +2
.nf
int AuthenticateMsg(unsigned char *auth_buffer, unsigned
                    char *buffer, unsigned int length)
{
    md5_calc(buffer, auth_buffer, length);

    return (0);
}
.fi
.in -2

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Committed
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.sp
.LP
.BR libmd5 (3LIB)
.sp
.LP
Rivest, R., The MD5 Message-Digest Algorithm, RFC 1321, April 1992.