Secret-Key Encryption Algorithms : Problem
Problem with secret-key algorithms is in the exchange of keys over an insecure channel.
1976 Diffie-Hellman Algorithm
- Grean and Brandon agree on a large prime number n and another number g.
These numbers do not neccesarily have to be secret.
- Brandon generates a random number x and sends Grean the value : A = gx mod n
- Grean generates a random number y and sends Brandon the value : B = gy mod n
- Brandon receives the value B and computes : Kx = Bx mod n
- Grean receives the value A and computes : Ky = Ay mod n
This algorithm ensure the values of Kx and Ky are equal and can be
used as the key in a secret-key encryption algorithm.
Since it is difficult to determin Kx (which = Ky) given the values of A and
B that could be intercepted, the value of the secret key is safe.
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Last Modified: June 1, 1997
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