Keeping secrets safe: modular arithmetic, RSA, entropy, hashing and error-correcting codes
Core operation of RSA encryption — raise a message to a power, modulo n.
Recovers the message using the private exponent d.
Counts integers below n coprime to it, for n = pq — used to make RSA keys.
Average information content — and the theoretical strength of a random source.
Bits of security from password length and character-set size.
Number of possible keys for a b-bit key.
Collisions become likely after about √ of the hash space.
Number of positions at which two strings differ.
Minimum parity bits r needed to protect m data bits.
Bitwise XOR of message and key; XOR again with k to decrypt.
Two parties derive the same secret over a public channel.
Time to try every key at a given guess rate.
A good hash flips about half its output bits when one input bit changes.
Shift each letter forward by k positions.
Approximate chance of a collision among n items in space N.