Cryptographic Chaining Mode

Cipher Chaining

ECB(electronic codebook) mode

• Same plain text produce the same cipher text
• No error propagation
• Residue is NO_HANDLE

plain text –CW encrypt–> cipher text
cipher text –CW decrypt–> plain text

CBC(cipher block chaining) mode

• Same plain text produce the different cipher text
• Error propagation to next block
• Need initialization vector

if A ^ B = Cthen C ^ A = B, C ^ B = A

p(n) xor iv/p(n-1) –CW encrypt–> c(n)
c(n) –CW decrypt–> xor iv/c(n-1) –> p(n)

Residue mode

ANSI(American National Standard Institute) SCTE(Society of Cable Telecommunications Engineers) 52

c(n-1) –>CW encrypt–> c’(n) –> xor short p(n) –> short c(n)
c(n-1) –>CW encrypt–> c’(n) –> xor short c(n) –> short p(n)

CTS(cipher text stealing)

encrypt:

Remain = sizeof(short p(n))
p’(n) = short p(n) + 0[Remain, Block_Len]
c(n) = c(x)[1, Remain]

p(n-1) xor c(n-2) –CW encrypt–> c(x) –> c(n)
p(n) –> p’(n) –> xor c(x) –> p(x) –CW encrypt–> c(n-1)

decrypt:

c(x) = short c(n) + p(x)[Remain+1, Block_Len]
p(n) = p’(n)[1, Remain]

c(n-1) –CW decrypt–> p(x) –> xor c(x) –> p’(n) –> short p(n)
c(x) –CW decrypt–> xor c(n-2) –> p(n-1)

CFB(cipher feedback) mode

• Same plain text produce the different cipher text.
• Need iv.
• Error propagation to next block.
• Residue is NO_HANDLE.

iv/c’(n-1) –CW encrypt–> c’(n) –> xor p(n) –> c(n)
iv/c’(n-1) –CW encrypt–> c’(n) –> xor c(n) –> p(n)

OFB(output feedback) mode

• Same plain text produce the different cipher text.
• Need iv.
• No error propagation.
• Residue is NO_HANDLE.
• One error bit of cipher text only cause one error bit of plain text.

iv/c’(n-1) –CW encrypt–> c’(n) –> xor p(n) –> c(n)
iv/c’(n-1) –CW encrypt–> c’(n) –> xor c(n) –> p(n)

CTR(counter) mode

• Same plain text produce the different cipher text.
• Need initialization counter.
• No error propagation.
• Residue is NO_HANDLE, but it’s cipher text.
• One error bit of cipher text only cause one error bit of plain text.

iv(n-1) – counter –> iv(n)
iv(n) –CW encrypt–> xor p(n) –> c(n)
iv(n) –CW encrypt–> xor c(n) –> p(n)

Reference:
https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation