The MD4 Message Digest Algorithm

Status of this Memo

This RFC is the specification of the MD4 Digest Algorithm. If you are going to implement MD4, it is suggested you do it this way. This memo is for informational use and does not constitute a standard. Distribution of this memo is unlimited.

Table of Contents

   1.  Abstract ....................................................    1
   2.  Terminology and Notation ....................................    2
   3.  MD4 Algorithm Description ...................................    2
   4.  Extensions ..................................................    6
   5.  Summary .....................................................    7
   6.  Acknowledgements ............................................    7
   APPENDIX - Reference Implementation .............................    7
   Security Considerations..........................................   18
   Author's Address.................................................   18

1. Abstract

This note describes the MD4 message digest algorithm. The algorithm takes as input an input message of arbitrary length and produces as output a 128-bit "fingerprint" or "message digest" of the input. It is conjectured that it is computationally infeasible to produce two messages having the same message digest, or to produce any message having a given prespecified target message digest. The MD4 algorithm is thus ideal for digital signature applications, where a large file must be "compressed" in a secure manner before being signed with the RSA public-key cryptosystem.

The MD4 algorithm is designed to be quite fast on 32-bit machines. On a SUN Sparc station, MD4 runs at 1,450,000 bytes/second. On a DEC MicroVax II, MD4 runs at approximately 70,000 bytes/second. On a 20MHz 80286, MD4 runs at approximately 32,000 bytes/second. In addition, the MD4 algorithm does not require any large substitution tables; the algorithm can be coded quite compactly.

The MD4 algorithm is being placed in the public domain for review and possible adoption as a standard.

(Note: The document supersedes an earlier draft. The algorithm described here is a slight modification of the one described in the draft.)

2. Terminology and Notation

In this note a "word" is a 32-bit quantity and a byte is an 8-bit quantity. A sequence of bits can be interpreted in a natural manner as a sequence of bytes, where each consecutive group of 8 bits is interpreted as a byte with the high-order (most significant) bit of each byte listed first. Similarly, a sequence of bytes can be interpreted as a sequence of 32-bit words, where each consecutive group of 4 bytes is interpreted as a word with the low-order (least significant) byte given first.

Let x_i denote "x sub i". If the subscript is an expression, we surround it in braces, as in x_{i+1}. Similarly, we use ^ for superscripts (exponentiation), so that x^i denotes x to the i-th power.

Let the symbol "+" denote addition of words (i.e., modulo- 2^32 addition). Let X <<< s denote the 32-bit value obtained by circularly shifting (rotating) X left by s bit positions. Let not(X) denote the bit-wise complement of X, and let X v Y denote the bit-wise OR of X and Y. Let X xor Y denote the bit-wise XOR of X and Y, and let XY denote the bit-wise AND of X and Y.

3. MD4 Algorithm Description

We begin by supposing that we have a b-bit message as input, and that we wish to find its message digest. Here b is an arbitrary nonnegative integer; b may be zero, it need not be a multiple of 8, and it may be arbitrarily large. We imagine the bits of the message written down as follows:

m_0 m_1 ... m_{b-1} .

The following five steps are performed to compute the message digest of the message.

Step 1. Append padding bits

The message is "padded" (extended) so that its length (in bits) is congruent to 448, modulo 512. That is, the message is extended so that it is just 64 bits shy of being a multiple of 512 bits long. Padding is always performed, even if the length of the message is already congruent to 448, modulo 512 (in which case 512 bits of padding are added).

Padding is performed as follows: a single "1" bit is appended to the message, and then enough zero bits are appended so that the length in bits of the padded message becomes congruent to 448, modulo 512.

Step 2. Append length

A 64-bit representation of b (the length of the message before the padding bits were added) is appended to the result of the previous step. In the unlikely event that b is greater than 2^64, then only the low-order 64 bits of b are used. (These bits are appended as two 32-bit words and appended low-order word first in accordance with the previous conventions.)

At this point the resulting message (after padding with bits and with b) has a length that is an exact multiple of 512 bits. Equivalently, this message has a length that is an exact multiple of 16 (32-bit) words. Let M[0 ... N-1] denote the words of the resulting message, where N is a multiple of 16.

Step 3. Initialize MD buffer

A 4-word buffer (A,B,C,D) is used to compute the message digest. Here each of A,B,C,D are 32-bit registers. These registers are initialized to the following values in hexadecimal, low-order bytes first):

            word A:    01 23 45 67
            word B:    89 ab cd ef
            word C:    fe dc ba 98
            word D:    76 54 32 10

Step 4. Process message in 16-word blocks

We first define three auxiliary functions that each take

as input three 32-bit words and produce as output one

32-bit word.

            f(X,Y,Z)  =  XY v not(X)Z
            g(X,Y,Z)  =  XY v XZ v YZ
            h(X,Y,Z)  =  X xor Y xor Z

In each bit position f acts as a conditional: if x then y else z. (The function f could have been defined using + instead of v since XY and not(X)Z will never have 1's in the same bit position.) In each bit position g acts as a majority function: if at least two of x, y, z are on, then g has a one in that bit position, else g has a zero. It is interesting to note that if the bits of X, Y, and Z are independent and unbiased, the each bit of f(X,Y,Z) will be independent and unbiased, and similarly each bit of g(X,Y,Z) will be independent and unbiased. The function h is the bit-wise "xor" or "parity" function; it has properties similar to those of f and g.

Do the following:

         For i = 0 to N/16-1 do  /* process each 16-word block */
         
                 For j = 0 to 15 do: /* copy block i into X */
                   Set X[j] to M[i*16+j].
                 end /* of loop on j */
                 Save A as AA, B as BB, C as CC, and D as DD.

[Round 1]

                   Let [A B C D i s] denote the operation
                         A = (A + f(B,C,D) + X[i]) <<< s  .
                   Do the following 16 operations:
                         [A B C D 0 3]
                         [D A B C 1 7]
                         [C D A B 2 11]
                         [B C D A 3 19]
                         [A B C D 4 3]
                         [D A B C 5 7]
                         [C D A B 6 11]
                         [B C D A 7 19]
                         [A B C D 8 3]
                         [D A B C 9 7]
                         [C D A B 10 11]
                         [B C D A 11 19]
                         [A B C D 12 3]
                         [D A B C 13 7]
                         [C D A B 14 11]
                         [B C D A 15 19]

[Round 2]

                   Let [A B C D i s] denote the operation
                         A = (A + g(B,C,D) + X[i] + 5A827999) <<< s .
                   (The value 5A..99 is a hexadecimal 32-bit
                   constant, written with the high-order digit
                   first. This constant represents the square
                   root of 2.  The octal value of this constant
                   is 013240474631.  See Knuth, The Art of
                   Programming, Volume 2 (Seminumerical
                   Algorithms), Second Edition (1981),
                   Addison-Wesley.  Table 2, page 660.)
                   Do the following 16 operations:
                         [A B C D 0  3]
                         [D A B C 4  5]
                         [C D A B 8  9]
                         [B C D A 12 13]
                         [A B C D 1  3]
                         [D A B C 5  5]
                         [C D A B 9  9]
                         [B C D A 13 13]
                         [A B C D 2  3]
                         [D A B C 6  5]
                         [C D A B 10 9]
                         [B C D A 14 13]
                         [A B C D 3  3]
                         [D A B C 7  5]
                         [C D A B 11 9]
                         [B C D A 15 13]

[Round 3]

                   Let [A B C D i s] denote the operation
                         A = (A + h(B,C,D) + X[i] + 6ED9EBA1) <<< s .
                   (The value 6E..A1 is a hexadecimal 32-bit
                   constant, written with the high-order digit
                   first.  This constant represents the square
                   root of 3.  The octal value of this constant
                   is 015666365641.  See Knuth, The Art of
                   Programming, Volume 2 (Seminumerical
                   Algorithms), Second Edition (1981),
                   Addison-Wesley.  Table 2, page 660.)
                   Do the following 16 operations:
                         [A B C D 0  3]
                         [D A B C 8  9]
                         [C D A B 4  11]
                         [B C D A 12 15]
                         [A B C D 2  3]
                         [D A B C 10 9]
                         [C D A B 6  11]
                         [B C D A 14 15]
                         [A B C D 1  3]
                         [D A B C 9  9]
                         [C D A B 5  11]
                         [B C D A 13 15]
                         [A B C D 3  3]
                         [D A B C 11 9]
                         [C D A B 7  11]
                         [B C D A 15 15]

Then perform the following additions:

                         A = A + AA
                         B = B + BB
         
                         C = C + CC
                         D = D + DD
         (That is, each of the four registers is incremented by
         the value it had before this block was started.)
         
         end /* of loop on i */
      
      Step 5. Output

The message digest produced as output is A,B,C,D. That is, we begin with the low-order byte of A, and end with the high-order byte of D.

This completes the description of MD4. A reference implementation in C is given in the Appendix.

4. Extensions

If more than 128 bits of output are required, then the following procedure is recommended to obtain a 256-bit output. (There is no provision made for obtaining more than 256 bits.)

Two copies of MD4 are run in parallel over the input. The first copy is standard as described above. The second copy is modified as follows.

The initial state of the second copy is:

                    word A:    00 11 22 33
                    word B:    44 55 66 77
                    word C:    88 99 aa bb
                    word D:    cc dd ee ff

The magic constants in rounds 2 and 3 for the second copy of MD4 are changed from sqrt(2) and sqrt(3) to cuberoot(2) and cuberoot(3):

Octal Hex

Round 2 constant 012050505746 50a28be6

Round 3 constant 013423350444 5c4dd124

Finally, after every 16-word block is processed (including the last block), the values of the A registers in the two copies are exchanged.

The final message digest is obtaining by appending the result of the second copy of MD4 to the end of the result of the first copy of MD4.

5. Summary

The MD4 message digest algorithm is simple to implement, and provides a "fingerprint" or message digest of a message of arbitrary length.

It is conjectured that the difficulty of coming up with two messages having the same message digest is on the order of 2^64 operations, and that the difficulty of coming up with any message having a given message digest is on the order of 2^128 operations. The MD4 algorithm has been carefully scrutinized for weaknesses. It is, however, a relatively new algorithm and further security analysis is of course justified, as is the case with any new proposal of this sort. The level of security provided by MD4 should be sufficient for implementing very high security hybrid digital signature schemes based on MD4 and the RSA public-key cryptosystem.

6. Acknowledgements

I'd like to thank Don Coppersmith, Burt Kaliski, Ralph Merkle, and Noam Nisan for numerous helpful comments and suggestions.

APPENDIX - Reference Implementation

This appendix contains the following files:

         md4.h        -- header file for using MD4 implementation
         md4.c        -- the source code for MD4 routines
         md4driver.c  -- a sample "user" routine
         session      -- sample results of running md4driver
 
 /*
 ** ********************************************************************
 ** md4.h -- Header file for implementation of                        **
 ** MD4 Message Digest Algorithm                                      **
 ** Updated: 2/13/90 by Ronald L. Rivest                              **
 ** (C) 1990 RSA Data Security, Inc.                                  **
 ** ********************************************************************
 */
 
 /* MDstruct is the data structure for a message digest computation.
 */
 typedef struct {
   unsigned int buffer[4]; /* Holds 4-word result of MD computation */
   unsigned char count[8]; /* Number of bits processed so far */
   unsigned int done;      /* Nonzero means MD computation finished */
 } MDstruct, *MDptr;
 
 /* MDbegin(MD)
 ** Input: MD -- an MDptr
 ** Initialize the MDstruct prepatory to doing a message digest
 ** computation.
 */
 extern void MDbegin();
 
 /* MDupdate(MD,X,count)
 ** Input: MD -- an MDptr
 **        X -- a pointer to an array of unsigned characters.
 **        count -- the number of bits of X to use (an unsigned int).
 ** Updates MD using the first "count" bits of X.
 ** The array pointed to by X is not modified.
 ** If count is not a multiple of 8, MDupdate uses high bits of
 ** last byte.
 ** This is the basic input routine for a user.
 ** The routine terminates the MD computation when count < 512, so
 ** every MD computation should end with one call to MDupdate with a
 ** count less than 512.  Zero is OK for a count.
 */
 extern void MDupdate();
 
 /* MDprint(MD)
 ** Input: MD -- an MDptr
 ** Prints message digest buffer MD as 32 hexadecimal digits.
 ** Order is from low-order byte of buffer[0] to high-order byte
 ** of buffer[3].
 ** Each byte is printed with high-order hexadecimal digit first.
 */
 extern void MDprint();
 
 /*
 ** End of md4.h
 ****************************(cut)***********************************/
 
 /*
 ** ********************************************************************
 ** md4.c -- Implementation of MD4 Message Digest Algorithm           **
 ** Updated: 2/16/90 by Ronald L. Rivest                              **
 ** (C) 1990 RSA Data Security, Inc.                                  **
 ** ********************************************************************
 */
 
 /*
 ** To use MD4:
 **   -- Include md4.h in your program
 **   -- Declare an MDstruct MD to hold the state of the digest
 **          computation.
 **   -- Initialize MD using MDbegin(&MD)
 **   -- For each full block (64 bytes) X you wish to process, call
 **          MDupdate(&MD,X,512)
 **      (512 is the number of bits in a full block.)
 **   -- For the last block (less than 64 bytes) you wish to process,
 **          MDupdate(&MD,X,n)
 **      where n is the number of bits in the partial block. A partial
 **      block terminates the computation, so every MD computation
 **      should terminate by processing a partial block, even if it
 **      has n = 0.
 **   -- The message digest is available in MD.buffer[0] ...
 **      MD.buffer[3].  (Least-significant byte of each word
 **      should be output first.)
 **   -- You can print out the digest using MDprint(&MD)
 */
 
 /* Implementation notes:
 ** This implementation assumes that ints are 32-bit quantities.
 ** If the machine stores the least-significant byte of an int in the
 ** least-addressed byte (e.g., VAX and 8086), then LOWBYTEFIRST
 ** should be set to TRUE.  Otherwise (e.g., SUNS), LOWBYTEFIRST
 ** should be set to FALSE.  Note that on machines with LOWBYTEFIRST
 ** FALSE the routine MDupdate modifies has a side-effect on its input
 ** array (the order of bytes in each word are reversed).  If this is
 ** undesired a call to MDreverse(X) can reverse the bytes of X back
 ** into order after each call to MDupdate.
 
 */
 #define TRUE  1
 #define FALSE 0
 #define LOWBYTEFIRST FALSE
 
 /* Compile-time includes
 */
 #include <stdio.h>
 #include "md4.h"
 
 /* Compile-time declarations of MD4 "magic constants".
 */
 #define I0  0x67452301       /* Initial values for MD buffer */
 #define I1  0xefcdab89
 #define I2  0x98badcfe
 #define I3  0x10325476
 #define C2  013240474631     /* round 2 constant = sqrt(2) in octal */
 #define C3  015666365641     /* round 3 constant = sqrt(3) in octal */
 /* C2 and C3 are from Knuth, The Art of Programming, Volume 2
 ** (Seminumerical Algorithms), Second Edition (1981), Addison-Wesley.
 ** Table 2, page 660.
 */
 #define fs1  3               /* round 1 shift amounts */
 #define fs2  7
 #define fs3 11
 #define fs4 19
 #define gs1  3               /* round 2 shift amounts */
 #define gs2  5
 #define gs3  9
 #define gs4 13
 #define hs1  3               /* round 3 shift amounts */
 #define hs2  9
 #define hs3 11
 #define hs4 15
 
 /* Compile-time macro declarations for MD4.
 ** Note: The "rot" operator uses the variable "tmp".
 ** It assumes tmp is declared as unsigned int, so that the >>
 ** operator will shift in zeros rather than extending the sign bit.
 */
 #define f(X,Y,Z)             ((X&Y) | ((~X)&Z))
 #define g(X,Y,Z)             ((X&Y) | (X&Z) | (Y&Z))
 #define h(X,Y,Z)             (X^Y^Z)
 #define rot(X,S)             (tmp=X,(tmp<<S) | (tmp>>(32-S)))
 #define ff(A,B,C,D,i,s)      A = rot((A + f(B,C,D) + X[i]),s)
 #define gg(A,B,C,D,i,s)      A = rot((A + g(B,C,D) + X[i] + C2),s)
 #define hh(A,B,C,D,i,s)      A = rot((A + h(B,C,D) + X[i] + C3),s)
 
 /* MDprint(MDp)
 ** Print message digest buffer MDp as 32 hexadecimal digits.
 ** Order is from low-order byte of buffer[0] to high-order byte of
 ** buffer[3].
 ** Each byte is printed with high-order hexadecimal digit first.
 ** This is a user-callable routine.
 */
 void
 MDprint(MDp)
 MDptr MDp;
 { int i,j;
   for (i=0;i<4;i++)
     for (j=0;j<32;j=j+8)
       printf("%02x",(MDp->buffer[i]>>j) & 0xFF);
 }
 
 /* MDbegin(MDp)
 ** Initialize message digest buffer MDp.
 ** This is a user-callable routine.
 */
 void
 MDbegin(MDp)
 MDptr MDp;
 { int i;
   MDp->buffer[0] = I0;
   MDp->buffer[1] = I1;
   MDp->buffer[2] = I2;
   MDp->buffer[3] = I3;
   for (i=0;i<8;i++) MDp->count[i] = 0;
   MDp->done = 0;
 }
 
 /* MDreverse(X)
 ** Reverse the byte-ordering of every int in X.
 ** Assumes X is an array of 16 ints.
 ** The macro revx reverses the byte-ordering of the next word of X.
 */
 #define revx { t = (*X << 16) | (*X >> 16); \
      *X++ = ((t & 0xFF00FF00) >> 8) | ((t & 0x00FF00FF) << 8); }
 MDreverse(X)
 unsigned int *X;
 { register unsigned int t;
   revx; revx; revx; revx; revx; revx; revx; revx;
   revx; revx; revx; revx; revx; revx; revx; revx;
 }
 
 /* MDblock(MDp,X)
 ** Update message digest buffer MDp->buffer using 16-word data block X.
 ** Assumes all 16 words of X are full of data.
 ** Does not update MDp->count.
 ** This routine is not user-callable.
 */
 static void
 MDblock(MDp,X)
 MDptr MDp;
 unsigned int *X;
 {
   register unsigned int tmp, A, B, C, D;
 #if LOWBYTEFIRST == FALSE
   MDreverse(X);
 #endif
   A = MDp->buffer[0];
   B = MDp->buffer[1];
   C = MDp->buffer[2];
   D = MDp->buffer[3];
   /* Update the message digest buffer */
   ff(A , B , C , D ,  0 , fs1); /* Round 1 */
   ff(D , A , B , C ,  1 , fs2);
   ff(C , D , A , B ,  2 , fs3);
   ff(B , C , D , A ,  3 , fs4);
   ff(A , B , C , D ,  4 , fs1);
   ff(D , A , B , C ,  5 , fs2);
   ff(C , D , A , B ,  6 , fs3);
   ff(B , C , D , A ,  7 , fs4);
   ff(A , B , C , D ,  8 , fs1);
   ff(D , A , B , C ,  9 , fs2);
   ff(C , D , A , B , 10 , fs3);
   ff(B , C , D , A , 11 , fs4);
   ff(A , B , C , D , 12 , fs1);
   ff(D , A , B , C , 13 , fs2);
   ff(C , D , A , B , 14 , fs3);
   ff(B , C , D , A , 15 , fs4);
   gg(A , B , C , D ,  0 , gs1); /* Round 2 */
   gg(D , A , B , C ,  4 , gs2);
   gg(C , D , A , B ,  8 , gs3);
   gg(B , C , D , A , 12 , gs4);
   gg(A , B , C , D ,  1 , gs1);
   gg(D , A , B , C ,  5 , gs2);
   gg(C , D , A , B ,  9 , gs3);
   gg(B , C , D , A , 13 , gs4);
   gg(A , B , C , D ,  2 , gs1);
   gg(D , A , B , C ,  6 , gs2);
   gg(C , D , A , B , 10 , gs3);
   gg(B , C , D , A , 14 , gs4);
   gg(A , B , C , D ,  3 , gs1);
   gg(D , A , B , C ,  7 , gs2);
   gg(C , D , A , B , 11 , gs3);
   gg(B , C , D , A , 15 , gs4);
   hh(A , B , C , D ,  0 , hs1); /* Round 3 */
   hh(D , A , B , C ,  8 , hs2);
   hh(C , D , A , B ,  4 , hs3);
   hh(B , C , D , A , 12 , hs4);
   hh(A , B , C , D ,  2 , hs1);
   hh(D , A , B , C , 10 , hs2);
   hh(C , D , A , B ,  6 , hs3);
   hh(B , C , D , A , 14 , hs4);
   hh(A , B , C , D ,  1 , hs1);
   hh(D , A , B , C ,  9 , hs2);
   hh(C , D , A , B ,  5 , hs3);
   hh(B , C , D , A , 13 , hs4);
   hh(A , B , C , D ,  3 , hs1);
   hh(D , A , B , C , 11 , hs2);
   hh(C , D , A , B ,  7 , hs3);
   hh(B , C , D , A , 15 , hs4);
   MDp->buffer[0] += A;
   MDp->buffer[1] += B;
   MDp->buffer[2] += C;
   MDp->buffer[3] += D;
 
 }
 
 /* MDupdate(MDp,X,count)
 ** Input: MDp -- an MDptr
 **        X -- a pointer to an array of unsigned characters.
 **        count -- the number of bits of X to use.
 **          (if not a multiple of 8, uses high bits of last byte.)
 ** Update MDp using the number of bits of X given by count.
 ** This is the basic input routine for an MD4 user.
 ** The routine completes the MD computation when count < 512, so
 ** every MD computation should end with one call to MDupdate with a
 ** count less than 512.  A call with count 0 will be ignored if the
 ** MD has already been terminated (done != 0), so an extra call with
 ** count 0 can be given as a "courtesy close" to force termination
 ** if desired.
 */
 void
 MDupdate(MDp,X,count)
 MDptr MDp;
 unsigned char *X;
 unsigned int count;
 { unsigned int i, tmp, bit, byte, mask;
   unsigned char XX[64];
   unsigned char *p;
   /* return with no error if this is a courtesy close with count
   ** zero and MDp->done is true.
   */
   if (count == 0 && MDp->done) return;
   /* check to see if MD is already done and report error */
   if (MDp->done)
          { printf("\nError: MDupdate MD already done."); return; }
   /* Add count to MDp->count */
   tmp = count;
   p = MDp->count;
   while (tmp)
     { tmp += *p;
       *p++ = tmp;
       tmp = tmp >> 8;
     }
   /* Process data */
   if (count == 512)
     { /* Full block of data to handle */
       MDblock(MDp,(unsigned int *)X);
     }
   else if (count > 512) /* Check for count too large */
     { printf("\nError: MDupdate called with illegal count value %d."
              ,count);
       return;
 
     }
   else /* partial block -- must be last block so finish up */
     { /* Find out how many bytes and residual bits there are */
       byte = count >> 3;
       bit =  count & 7;
       /* Copy X into XX since we need to modify it */
       for (i=0;i<=byte;i++)   XX[i] = X[i];
       for (i=byte+1;i<64;i++) XX[i] = 0;
       /* Add padding '1' bit and low-order zeros in last byte */
       mask = 1 << (7 - bit);
       XX[byte] = (XX[byte] | mask) & ~( mask - 1);
       /* If room for bit count, finish up with this block */
       if (byte <= 55)
         { for (i=0;i<8;i++) XX[56+i] = MDp->count[i];
           MDblock(MDp,(unsigned int *)XX);
         }
       else /* need to do two blocks to finish up */
         { MDblock(MDp,(unsigned int *)XX);
           for (i=0;i<56;i++) XX[i] = 0;
           for (i=0;i<8;i++)  XX[56+i] = MDp->count[i];
           MDblock(MDp,(unsigned int *)XX);
         }
       /* Set flag saying we're done with MD computation */
       MDp->done = 1;
     }
 }
 
 /*
 ** End of md4.c
 ****************************(cut)***********************************/
 
 /*
 ** ********************************************************************
 ** md4driver.c -- sample routines to test                            **
 ** MD4 message digest algorithm.                                     **
 ** Updated: 2/16/90 by Ronald L. Rivest                              **
 ** (C) 1990 RSA Data Security, Inc.                                  **
 ** ********************************************************************
 */

#include <stdio.h>
#include "md4.h"

 /* MDtimetrial()
 ** A time trial routine, to measure the speed of MD4.
 ** Measures speed for 1M blocks = 64M bytes.
 */
 MDtimetrial()
 { unsigned int X[16];
   MDstruct MD;
   int i;
   double t;
   for (i=0;i<16;i++) X[i] = 0x01234567 + i;
   printf
   ("MD4 time trial. Processing 1 million 64-character blocks...\n");
   clock();
   MDbegin(&MD);
   for (i=0;i<1000000;i++) MDupdate(&MD,X,512);
   MDupdate(&MD,X,0);
   t = (double) clock(); /* in microseconds */
   MDprint(&MD); printf(" is digest of 64M byte test input.\n");
   printf("Seconds to process test input:   %g\n,t/1e6);
   printf("Characters processed per second: %ld.\n,(int)(64e12/t));
 }
 
 /* MDstring(s)
 ** Computes the message digest for string s.
 ** Prints out message digest, a space, the string (in quotes) and a
 ** carriage return.
 */
 MDstring(s)
 unsigned char *s;
 { unsigned int i, len = strlen(s);
   MDstruct MD;
   MDbegin(&MD);
   for (i=0;i+64<=len;i=i+64) MDupdate(&MD,s+i,512);
   MDupdate(&MD,s+i,(len-i)*8);
   MDprint(&MD);
   printf(" \"%s\"\n",s);
 }
 
 /* MDfile(filename)
 ** Computes the message digest for a specified file.
 ** Prints out message digest, a space, the file name, and a
 ** carriage return.
 */
 MDfile(filename)
 char *filename;
 { FILE *f = fopen(filename,"rb");
   unsigned char X[64];
   MDstruct MD;
   int b;
   if (f == NULL)
      { printf("%s can't be opened.\n",filename); return; }
   MDbegin(&MD);
   while ((b=fread(X,1,64,f))!=0) MDupdate(&MD,X,b*8);
 
   MDupdate(&MD,X,0);
   MDprint(&MD);
   printf(" %s\n",filename);
   fclose(f);
 }
 
 /* MDfilter()
 ** Writes the message digest of the data from stdin onto stdout,
 ** followed by a carriage return.
 */
 MDfilter()
 { unsigned char X[64];
   MDstruct MD;
   int b;
   MDbegin(&MD);
   while ((b=fread(X,1,64,stdin))!=0) MDupdate(&MD,X,b*8);
   MDupdate(&MD,X,0);
   MDprint(&MD);
   printf("\n");
 }
 
 /* MDtestsuite()
 ** Run a standard suite of test data.
 */
 MDtestsuite()
 {
   printf("MD4 test suite results:\n");
   MDstring("");
   MDstring("a");
   MDstring("abc");
   MDstring("message digest");
   MDstring("abcdefghijklmnopqrstuvwxyz");
   MDstring
   ("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789");
   MDfile("foo"); /* Contents of file foo are "abc" */
 }
 
 main(argc,argv)
 int argc;
 char *argv[];
 { int i;
   /* For each command line argument in turn:
   ** filename          -- prints message digest and name of file
   ** -sstring          -- prints message digest and contents of string
   ** -t                -- prints time trial statistics for 64M bytes
   ** -x                -- execute a standard suite of test data
   ** (no args)         -- writes messages digest of stdin onto stdout
   */
 
   if (argc==1) MDfilter();
   else
     for (i=1;i<argc;i++)
       if (argv[i][0]=='-' && argv[i][1]=='s') MDstring(argv[i]+2);
       else if (strcmp(argv[i],"-t")==0)       MDtimetrial();
       else if (strcmp(argv[i],"-x")==0)       MDtestsuite();
       else                                    MDfile(argv[i]);
 }
 
 /*
 ** end of md4driver.c
 ****************************(cut)***********************************/
 
 --------------------------------------------------------------------
 --- Sample session.  Compiling and using MD4 on SUN Sparcstation ---
 --------------------------------------------------------------------
 >ls
 total 66
 -rw-rw-r--  1 rivest          3 Feb 14 17:40 abcfile
 -rwxrwxr-x  1 rivest      24576 Feb 17 12:28 md4
 -rw-rw-r--  1 rivest       9347 Feb 17 00:37 md4.c
 -rw-rw-r--  1 rivest      25150 Feb 17 12:25 md4.doc
 -rw-rw-r--  1 rivest       1844 Feb 16 21:21 md4.h
 -rw-rw-r--  1 rivest       3497 Feb 17 12:27 md4driver.c
 >
 >cc -o md4 -O4 md4.c md4driver.c
 md4.c:
 md4driver.c:
 Linking:
 >
 >md4 -x
 MD4 test suite results:
 31d6cfe0d16ae931b73c59d7e0c089c0 ""
 bde52cb31de33e46245e05fbdbd6fb24 "a"
 a448017aaf21d8525fc10ae87aa6729d "abc"
 d9130a8164549fe818874806e1c7014b "message digest"
 d79e1c308aa5bbcdeea8ed63df412da9 "abcdefghijklmnopqrstuvwxyz"
 043f8582f241db351ce627e153e7f0e4
      "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
 a448017aaf21d8525fc10ae87aa6729d abcfile
 >
 >md4 -sabc -shi
 a448017aaf21d8525fc10ae87aa6729d "abc"
 cfaee2512bd25eb033236f0cd054e308 "hi"
 >
 >md4 *
 a448017aaf21d8525fc10ae87aa6729d abcfile
 d316f994da0e951cf9502928a1f73300 md4
 379adb39eada0dfdbbdfdcd0d9def8c4 md4.c
 9a3f73327c65954198b1f45a3aa12665 md4.doc
 37fe165ac177b461ff78b86d10e4ff33 md4.h
 7dcba2e2dc4d8f1408d08beb17dabb2a md4.o
 08790161bfddc6f5788b4353875cb1c3 md4driver.c
 1f84a7f690b0545d2d0480d5d3c26eea md4driver.o
 >
 >cat abcfile | md4
 a448017aaf21d8525fc10ae87aa6729d
 >
 >md4 -t
 MD4 time trial. Processing 1 million 64-character blocks...
 6325bf77e5891c7c0d8104b64cc6e9ef is digest of 64M byte test input.
 Seconds to process test input:   44.0982
 Characters processed per second: 1451305.
 >
 >
 ------------------------ end of sample session --------------------
 
      Note:  A version of this document including the C source code is
      available for FTP from THEORY.LSC.MIT.EDU in the file "md4.doc".

Security Considerations

The level of security discussed in this memo by MD4 is considered to be sufficient for implementing very high security hybrid digital signature schemes based on MD4 and the RSA public-key cryptosystem.

Author's Address

Ronald L. Rivest
Massachusetts Institute of Technology
Laboratory for Computer Science
NE43-324
545 Technology Square
Cambridge, MA 02139-1986

Phone:

          (617) 253-5880
   
   EMail: rivest@theory.lcs.mit.edu