Tiny Encryption Algorithm

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The Tiny Encryption Algorithm, or TEA [1] is a block cipher designed for small size and easy software implementation. It is a Feistel cipher with 64-bit blocks, a 128-bit key, 32 rounds and a very simple round function using only 32-bit operations -- addition, bitwise XOR and shift. In C, the encryption and decryption routines are under 10 lines each. No S-boxes are used, so the data space required is also tiny.

TEA has some weaknesses. Equivalent keys are one problem; each key is equivalent to three others, so the effective key size is only 126 bits. [2]. As a result, TEA is weak if used to build a cryptographic hash. This weakness led to a method for hacking Microsoft's Xbox game console, where the cipher was used as a hash function. [3] TEA is also susceptible to a related-key attack which requires 223 chosen plaintexts under a related-key pair, with 232 time complexity [4].

Partly because of these weaknesses, a number of revisions of TEA have been designed. Block TEA or XTEA extends TEA to build a variable block size cipher. XXTEA is a later revision.

The cipher is freely available for any use. It has a home page.

## References[edit]

1. ↑ David J. Wheeler, Roger M. Needham (1994), TEA, a Tiny Encryption Algorithm
2. ↑ Kelsey, John (1996), "Key-schedule cryptanalysis of IDEA, G-DES, GOST, SAFER, and Triple-DES", Lecture Notes in Computer Science 1109: 237–251, DOI:10.1007/3-540-68697-5_19
3. ↑ Michael Steil. 17 Mistakes Microsoft Made in the Xbox Security System.
4. ↑ Kelsey, John (1997), "Related-key cryptanalysis of 3-WAY, Biham-DES, CAST, DES-X NewDES, RC2, and TEA", Lecture Notes in Computer Science 1334: 233–246, DOI:10.1007/BFb0028479