Residual block termination

In cryptography, residual block termination is a variation of cipher block chaining mode (CBC) that does not require any padding. It does this by effectively changing to cipher feedback mode for one block. The cost is the increased complexity.

Encryption procedure

If the plaintext length N is not a multiple of the block size L:

Encrypt the ⌊N/L⌋ full blocks of plaintext using the cipher block chaining mode;
Encrypt the last full encrypted block again;
XOR the remaining bits of the plaintext with leftmost bits of the re-encrypted block.

Decryption procedure

Decrypt the ⌊N/L⌋ full encrypted blocks using the Cipher Block Chaining mode;
Encrypt the last full encrypted block;
XOR the remaining bits of the ciphertext with leftmost bits of the re-encrypted block.

Short message

For messages shorter than one block, residual block termination can use an encrypted IV instead of the previously encrypted block.

Block ciphers (security summary)
Common algorithms	AES Blowfish DES (internal mechanics, Triple DES) Serpent Twofish
Less common algorithms	ARIA Camellia CAST-128 GOST IDEA LEA RC2 RC5 RC6 SEED Skipjack TEA XTEA
Other algorithms	3-Way Akelarre Anubis BaseKing BassOmatic BATON BEAR and LION CAST-256 Chiasmus CIKS-1 CIPHERUNICORN-A CIPHERUNICORN-E CLEFIA CMEA Cobra COCONUT98 Crab Cryptomeria/C2 CRYPTON CS-Cipher DEAL DES-X DFC E2 FEAL FEA-M FROG G-DES Grand Cru Hasty Pudding cipher Hierocrypt ICE IDEA NXT Intel Cascade Cipher Iraqi Kalyna KASUMI KeeLoq KHAZAD Khufu and Khafre KN-Cipher Kuznyechik Ladder-DES Libelle LOKI (97, 89/91) Lucifer M6 M8 MacGuffin Madryga MAGENTA MARS Mercy MESH MISTY1 MMB MULTI2 MultiSwap New Data Seal NewDES Nimbus NOEKEON NUSH PRESENT Prince Q REDOC Red Pike S-1 SAFER SAVILLE SC2000 SHACAL SHARK Simon SM4 Speck Spectr-H64 Square SXAL/MBAL Threefish Treyfer UES xmx XXTEA Zodiac
Design	Feistel network Key schedule Lai–Massey scheme Product cipher S-box P-box SPN Confusion and diffusion Avalanche effect Block size Key size Key whitening (Whitening transformation)
Attack (cryptanalysis)	Brute-force (EFF DES cracker) MITM Biclique attack 3-subset MITM attack Linear (Piling-up lemma) Differential Impossible Truncated Higher-order Differential-linear Distinguishing (Known-key) Integral/Square Boomerang Mod n Related-key Slide Rotational Side-channel Timing Power-monitoring Electromagnetic Acoustic Differential-fault XSL Interpolation Partitioning Rubber-hose Black-bag Davies Rebound Weak key Tau Chi-square Time/memory/data tradeoff
Standardization	AES process CRYPTREC NESSIE
Utilization	Initialization vector Mode of operation Padding

Cryptography
History of cryptography Cryptanalysis Outline of cryptography
Symmetric-key algorithm Block cipher Stream cipher Public-key cryptography Cryptographic hash function Message authentication code Random numbers Steganography
Category

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