1

RSA

Rivest Shamir Adelman: Patented in 1983, expired in 2000

Based on difficulty of factorization

Choose two large random prime numbers p and q,

Compute n = p*q

Compute φ(n) = (p-1)(q-1)

Choose an integer e, such that e, is coprime to φ(n)

-- e, is released as the public key

Compute d, to satisfy (d*e) mod φ(n) = 1

-- d, is kept as the private key

2

RSA

Encryption (of message m)

(m)e mod n

Decryption (of cipher m’)

(m’)e mod n

RSA property

((m)e)d mod n = m