Create README.txt

Author: sirdarckcat

block2/README.txt

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+block2
+======
+
+This code produces the second block of an MD5 collision given the chaining
+value from a first block message.  Using the chaining value from M output
+by the block1 program, we are able to calculate the chaining value for M1'. 
+The chaining values are specified in the file 'CV.txt'.
+
+Compilation instructions
+========================
+	g++ -O3 -c md5.cpp
+	g++ -O3 -c block2.cpp
+	g++ block2.o md5.o -o Block2.out
+	
+At one point we noted that compiling the Block2 code with the Intel compiler
+produced a 30% performance increase.  People having access to the Intel 
+compiler are encouraged to use it.
+
+icc -fast -Ob2 md5.cpp block2.cpp
+The binary will be placed in a.out
+
+
+
+Sufficient Conditions
+======================
+
+The sufficient conditions for producing a second block message are
+contained in md5cond2.txt.  Conditions reflect the updated conditions
+released by Jun Yajima and Takeshi Shemoyama.  These conditions may
+be modified by researchers when the list of sufficient conditions
+is changed.  It should also be noted that conditions are "manually"
+satisfied for portions of the code rather than looking through the list
+of condtions for efficiency reasons.  In md5cond2.txt each condition is
+represented by a three tuple (x,y,z).  x is the step value the condition
+is placed on and has value [0-63].  y is the bit within the step value
+that the condition is placed on, and has values [1-32].  z is the type
+of condition having value [0-6]
+
+0	-bit y of stepvalue x should be 0
+1	-bit y of stepvalue x should be 1
+2	-bit y of stepvalue x should be equal to bit y of stepvalue x-1
+3	-bit y of stepvalue x should be equal to bit y of stepvalue x-2
+4	-bit y of stepvalue x should be not equal to bit y of stepvalue x-1
+5	-bit y of stepvalue x should be not equal to bit y of stepvalue x-2
+
+
+
+Chaining Values
+===============
+CV.txt may have arbitrarily many chaining values.
+
+First-block chaining values are used as the IV's for the second block.
+Each set of chainging values is specified on a single line as a 128 bit value.
+
+
+Executing block2 code
+=====================
+
+block2
+block2 [num cv]
+block2 [num cv] [num coll]
+
+where:
+	[num cv] is the number of chaining value sets to be read from CV.txt
+	
+	[num coll] is the number of collisions to be produced for each 
+	chainging variable.
+	
+	When [num coll] is specified [num cv] must also be specified.
+	When either [num coll] or both parameters are not specified they
+	default to 1.
+
+
+Output Format
+=============
+
+The output format is the same for block2 as it is for block1: the chaining
+value for M is output first, then M and M' are output.  Here they are 
+two 512-bit values intended as the second blocks corresponding to the
+pair output from the block1 code.
+
+The chaining value shown is NOT the same as the MD5 output value when
+run on either colliding pair because our calculations were not done with
+the length appended.  However, since both messages are two blocks long,
+appending the length will not upset the collision.
+
+
+
+Debugging
+=========
+
+Optional output has been left in the code for the purpose of dubugging.  This
+output can be turned on by setting the DEBUG constant to 1 rather than 0.