Explanation

Key Schedule

https://en.wikipedia.org/wiki/Key_schedule

In cryptography, the so-called product ciphers are a certain kind of cipher, where the (de-)ciphering of data is typically done as an iteration of rounds. The setup for each round is generally the same, except for round-specific fixed values called a round constant, and round-specific data derived from the cipher key called a round key. A key schedule is an algorithm that calculates all the round keys from the key.

Explanation

DSA

https://en.wikipedia.org/wiki/Digital_Signature_Algorithm

DSA is covered by U.S. Patent 5,231,668 , filed July 26, 1991 and now expired, and attributed to David W. Kravitz, a former NSA employee. This patent was given to " The United States of America as represented by the Secretary of Commerce, Washington, D.C. " , and NIST has made this patent available worldwide royalty-free. Claus P. Schnorr claims that his U.S. Patent 4,995,082 (also now expired) covered DSA; this claim is disputed.

Substitution

https://en.wikipedia.org/wiki/Atbash

Atbash is a monoalphabetic substitution cipher originally used to encrypt the Hebrew alphabet. It can be modified for use with any known writing system with a standard collating order.

Explanation

Kerberos

https://en.wikipedia.org/wiki/Kerberos_(protocol)

Kerberos is a computer-network authentication protocol that works on the basis of tickets to allow nodes communicating over a non-secure network to prove their identity to one another in a secure manner. The protocol was named after the character Kerberos (or Cerberus) from Greek mythology, the ferocious three-headed guard dog of Hades. Its designers aimed it primarily at a client–server model and it provides mutual authentication—both the user and the server verify each other ' s identity. Kerberos protocol messages are protected against eavesdropping and replay attacks.

Kerberos builds on symmetric key cryptography and requires a trusted third party, and optionally may use public-key cryptography during certain phases of authentication. Kerberos uses UDP port 88 by default.

IDEA

https://en.wikipedia.org/wiki/International_Data_Encryption_Algorithm

In cryptography, the International Data Encryption Algorithm (IDEA), originally called Improved Proposed Encryption Standard (IPES), is a symmetric-key block cipher designed by James Massey of ETH Zurich and Xuejia Lai and was first described in 1991. The algorithm was intended as a replacement for the Data Encryption Standard (DES). IDEA is a minor revision of an earlier cipher Proposed Encryption Standard (PES).

The cipher was designed under a research contract with the Hasler Foundation, which became part of Ascom-Tech AG. The cipher was patented in a number of countries but was freely available for non-commercial use. The name " IDEA " is also a trademark. The last patents expired in 2012, and IDEA is now patent-free and thus completely free for all uses.

IDEA was used in Pretty Good Privacy (PGP) v2.0 and was incorporated after the original cipher used in v1.0, BassOmatic, was found to be insecure. IDEA is an optional algorithm in the OpenPGP standard.

Explanation

4

https://en.wikipedia.org/wiki/Feistel_cipher

Michael Luby and Charles Rackoff analyzed the Feistel cipher construction, and proved that if the round function is a cryptographically secure pseudorandom function, with Ki used as the seed, then 3 rounds are sufficient to make the block cipher a pseudorandom permutation, while 4 rounds are sufficient to make it a " strong " pseudorandom permutation (which means that it remains pseudorandom even to an adversary who gets oracle access to its inverse permutation). Because of this very important result of Luby and Rackoff, Feistel ciphers are sometimes called Luby–Rackoff block ciphers.

Joan’s public key

https://en.wikipedia.org/wiki/RSA_(cryptosystem)

Suppose Joahn uses Bob ' s public key to send him an encrypted message. In the message, she can claim to be Alice but Bob has no way of verifying that the message was actually from Alice since anyone can use Bob ' s public key to send him encrypted messages. In order to verify the origin of a message, RSA can also be used to sign a message.

Suppose Alice wishes to send a signed message to Bob. She can use her own private key to do so. She produces a hash value of the message, raises it to the power of d (modulo n) (as she does when decrypting a message), and attaches it as a " signature " to the message. When Bob receives the signed message, he uses the same hash algorithm in conjunction with Alice ' s public key. He raises the signature to the power of e (modulo n) (as he does when encrypting a message), and compares the resulting hash value with the message ' s actual hash value. If the two agree, he knows that the author of the message was in possession of Alice ' s private key, and that the message has not been tampered with since.