# RC5 block-cipher

Library implementation of the basic RC5 block cipher in Rust. RC5 is different from the classical ciphers (like AES) in the sense that allows to parametrize the algorithm and optimize both security and efficiency on different hardware.

These parameters are:

• w: word length in bytes
• r: number of rounds

• b: key length in bytes

  The selection of each of them should be preferably done by choosing standards from other use cases. For example the word length w could be any number of bytes but the recommendation for performance and security is that should be a power of 2, or even better, a power of 8. In that way one can use the hardware registers more efficiently, e.g. 32-bits or 64-bits registers, with vectorization possibilities (AVX on Intel or SVE on ARM).

  This RC5 implementation is designed only for the standard values of w (powers of 8) making use of the standard Rust types: u8, u16, u32, u64, u128.

  Example: encryption

  ```rust use rc5_cipher::encode;

  let key = vec![ 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, ]; let pt = vec![0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77]; let ct = vec![0x2D, 0xDC, 0x14, 0x9B, 0xCF, 0x08, 0x8B, 0x9E];

  let res = encode::(key, pt); assert_eq!(ct, res.unwrap()); ```

  Example: decryption

  ```rust use rc5_cipher::decode;

  let key = vec![ 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, ]; let pt = vec![0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77]; let ct = vec![0x2D, 0xDC, 0x14, 0x9B, 0xCF, 0x08, 0x8B, 0x9E];

  let res = decode::(key, ct); assert_eq!(pt, res.unwrap()); ```

  Bibliography

• Rivest original paper: https://www.grc.com/r&d/rc5.pdf

• C implementation and tests: https://tools.ietf.org/id/draft-krovetz-rc6-rc5-vectors-00.html#rfc.section.4
• Haskell implementation: https://hackage.haskell.org/package/cipher-rc5-0.1.1.2/docs/src/Crypto-Cipher-RC5.html