cryptography

last edited Sat, 20 Jul 2024 11:31:53 GMT
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the science of secrecy is largely a secret science

While authentication keys tend to expire once changed or during single use, decryption keys can remain detrimental to security due to their persistent value in decrypting ciphertext corresponding to those exact keys.^[1] In other words, as long as ciphertext is widely available, access to its corresponding decryption key is a security risk. authenticity and confidentiality are different concepts.

Ciphers direct link to this section

Ciphers are broken in secret, opponents will not announce. Using one type of Cipher is allowing a single point of failure because we cannot measure cipher strength. ^[2]

Block Cipher direct link to this section

Stream Cipher direct link to this section

Often described as a symmetric encryption algorithm such that:

• length of the output is equal to the length of the input
• for any n, the first n output bits depend on the key and the first n input bits.

One-Time Pad direct link to this section

Also known as Vernam-cipher, messages are encrypted with randomized data. For a 5 letter text, the possibilities to brute force would be 26^5. The security of OTP relies on randomless of the key. Despite being broken in other applications before, it is said to be unbreakable (officially). If any of the following rules are broken then OTP is no longer unbreakable. ^[3] OTP is said to have perfect secrecy

• The key is at least as long as the message or data that must be encrypted.
• The key is truly random (not generated by a simple computer function or such)
• Key and plaintext are calculated modulo 10 (digits), modulo 26 (letters) or modulo 2 (binary)
• Each key is used only once, and both sender and receiver must destroy their key after use.
• There should only be two copies of the key: one for the sender and one for the receiver (some exceptions exist for multiple receivers).