question on MD5 state variables.

Question

Hi,

I am studying MD5 algorithm. I found out that there are four state variables (I am not sure what that means). Those variables are 0x67452301 , 0xEFCDAB89, 0x98BADCFE, and 0x10325476. I converted variables to decimals and came up with 1732584193, 4023233417, 2562383102, and 271733878 resepectively.

my question is, why those numbers? Are they special numbers?

Answer 1

See RFC 1321, section 3.3:

3.3 Step 3. Initialize MD Buffer

A four-word buffer (A,B,C,D) is used to compute the message digest. Here each of A, B, C, D is a 32-bit register. 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

The numbers they picked are just ascending and descending single hexadecimal digits, in order (which seems to be a delightfully arbitrary set of initial values).

Since they wrote the low-order bytes first, when you write it with the least significant bytes on the right, you get 0x67452301, etc.