Symmetric Key Cryptography Flashcards
Electronic Code Book Mode (ECB)
Encrypts 64bit blocks of plain text using a set key. The same plain text repeated would result in the same cipher text. Not secure.
Cipher block chaining mode (CBC)
XORs the plain text blocks with the preceding block of text. Uses initialization vector (IV). Issue is errors propagate because of the chaining process.
Cipher feedback mode (CFB)
Streaming version of CBC.
Output Feedback mode (OFB)
Same is CFB, but uses a seed value to XOR the plaintext rather than using the previous block of text. There is no chaining process so errors don’t propogate.
Counter Mode (CTR)
Similar to OFB but doesn’t use a seed value for encryption process. It uses a counter value. Also doesn’t using chaining.
Galois/Counter Mode (GCM)
Similar to Counter Mode (CTR), but also includes data authenticity using authentication tags.
Counter with Cipher Block Chaining Message Authentication Code Mode (CCM)
Provides confidentiality and authenticity using a combination of CTR and CBC. Only used with 128 bit blocks. Used with a nonce that is changed each time.
Nonce
Number used once. usually randomly generated
Data Encryption Standard (DES)
US created it in 1977 and is no longer secure. Basis for 3DES. 56bit key and 64bit block.
Triple DES (3DES)
168bit key. Not secure. No longer in use by gov’t agencies by end of 2023.
International Data Encryption Algorithm (IDEA)
128 bit key. Used in PGP. Applied to 64bit blocks.
Blowfish
Variable key length up to 448 bit. Applied to 64bit blocks of data. Free for use.
Skipjack
80 bit key applied to 64bit blocks. Approved by US FIPS as the escrow encryption standard (EES). NIST and Dept of Treasury hold half of the key so they can decrypt the data if needed. Not used much because entities don’t trust escrow.
Rivest Cipher 4 (RC4)
Stream cipher with variable length key between 40 and 2048. Was used in WEP, WPA, SSL and TLS. No longer secure.
RC5
Variable block cipher (32, 64, 128). Variable key length 0 to 2040. A singled message was cracked in 4 years.