The Diffe-Hellman key exchange algorithm

This is Simon explaining Diffe-Hellman key exchange (also called DiffeHellman protocol). He first explained the algorithm mixing watercolours (a color representing a key/ number) and then mathematically. The algorithm allows two parties (marked “you” and “your friend” in Simon’s diagram) with no prior knowledge of each other to establish a shared secret key over an insecure channel (a public area or an “eavesdropper”). This key can then be used to encrypt subsequent communications using a symmetric keycipher. Simon calls it “a neat algorithm”). Later the same night, he also gave me a lecture on a similar but more complicated algorithm called the RSA. Simon first learned about this on Computerphile and then also saw a video about the topic on MajorPrep. And here is another MajorPrep video on modular arithmetic.

originally there are two private keys (a and b) and one public key g
Neva helping Simon to mix the colors representing each key
Mixing g and b to create the public key for b
Mixing the public and the private keys to create a unique shared key
Done!Both a and b have a unique shared key (purplish)
Simon now expressed the same in mathematical formulas
Simon explained that the ≡ symbol (three stripes) means congruence in its modular arithmetic meaning (if a and b are congruent modulo n, they have no difference in modular arithmetic under modulo n)

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