respected sir, i am a student(B.E,electronics) of M S University,Baroda,India.my name is kurang mehta. as my final year project i am implementing voice encryption algorithm using the dsp kit tms320c5x. i came across your reference by surfing the net. i have implemented the rc5 encryption algorithm but the decryption part is becoming a problem for me. i am herewith sending you the encryption algorithm: We assume that the input block is given in two w-bit registers A and B. We also assume that key-expansion has already been performed, so that the array S[0...t-1] has been computed. Below is the encryption algorithm in pseudo-code. The output is also placed in registers A and B. A = A + S[0]; B = B + S[1]; FOR i = 1 TO r DO A = ((A [Image] B) <<< B) + S[2*i]; B = ((B [Image] A) <<< A) + S[2*i+1]; The key expansion is also performed as showm below:(Image is any constant) The first algorithmic step of key expansion is to copy the secret key K[0...b-1] into an array L[0...c-1] of c = [Image] words, where u=w/8 is the number of bytes/word. This operation is done in a natural manner, using u consecutive key bytes of K to fill up each successive word in L, low-order byte to high-order byte. Any unfilled byte positions of L are zeroed. The second algorithmic step of key expansion is to initialize array S to a particular fixed (key-independent) pseudo-random bit pattern, using an arithmetic progression modulo [Image] determined by the "magic constants" [Image] and [Image]. Since [Image] is odd, the arithmetic progression has period [Image]. S[0] = [Image]; FOR i = 1 TO t-1 DO S[i] = S[i-1] + [Image]; The third algorithmic step of key expansion is to mix in the user's secret key in three passes over the arrays S and L. More precisely, due to the potentially different sizes of S and L, the larger array will be processed three times, and the other may be handled more times. i = j = 0; A = B = 0; DO 3*max(t,c) TIMES: A = S[i] = (S[i] + A + B) <<< 3; B = L[j] = (L[j] + A + B) <<< (A+B); i = (i + 1) mod(t); j = (j + 1) mod(c); The key-expansion function has a certain amount of "one-wayness": it is not so easy to determine K from S. Now if possible i would like to get some help from you regarding the rc5 decryption algorithm (in the form of source code or c language). awaiting a response at the earliest. sincerely yours kurang