Tiny Encryption Algorithm

Infobox block cipher
name = TEA


caption = Two Feistel rounds (one cycle) of TEA
designers = Roger Needham, David Wheeler
publish date = 1994
derived from =
derived to = XTEA
key size = 128 bits
block size = 64 bits
structure = Feistel network
rounds = variable; recommended 64 Feistel rounds (32 cycles)
cryptanalysis = TEA suffers from equivalent keys (Kelsey et al, 1996) and can be broken using a related-key attack requiring 2²³ chosen plaintexts and a time complexity of 2³².

In cryptography, the Tiny Encryption Algorithm (TEA) is a block cipher notable for its simplicity of description and implementation (typically a few lines of code). It was designed by David Wheeler and Roger Needham of the Cambridge Computer Laboratory, and first presented at the Fast Software Encryption workshop in 1994. [cite journal | first = David J. | last = Wheeler | coauthors = Needham, Roger M. | url = http://citeseer.ist.psu.edu/102148.html
title = TEA, a tiny encryption algorithm | publisher = Fast Software Encryption: Second International Workshop | volume = 1008 | journal = Lecture Notes in Computer Science | pages = 363–366 | location = Leuven, Belgium | date = 1994-12-16]

The cipher is not subject to any patents.

Properties

TEA operates on 64-bit blocks and uses a 128-bit key. It has a Feistel structure with a suggested 64 rounds, typically implemented in pairs termed "cycles". It has an extremely simple key schedule, mixing all of the key material in exactly the same way for each cycle. Different multiples of a magic constant are used to prevent simple attacks based on the symmetry of the rounds. The magic constant, 2654435769 or $mathrm\{9E3779B9\_\{16$ is chosen to be $lfloor\; 2^\{32\}/phi\; floor$ where $phi,$ is the golden ratio.

TEA has a few weaknesses. Most notably, it suffers from equivalent keys — each key is equivalent to three others, which means that the effective key size is only 126 bits. cite journal | first = John | last = Kelsey | coauthors = Schneier, Bruce; Wagner, David | url = http://www.schneier.com/paper-key-schedule.pdf
title = Key-schedule cryptanalysis of IDEA, G-DES, GOST, SAFER, and Triple-DES | journal = Lecture Notes in Computer Science | volume = 1109 | pages = 237–251 | date = 1996 | doi = 10.1007/3-540-68697-5_19] As a result, TEA is especially bad as a cryptographic hash function. This weakness led to a method for hacking Microsoft's Xbox game console, where the cipher was used as a hash function. [cite web |url=http://www.xbox-linux.org/wiki/17_Mistakes_Microsoft_Made_in_the_Xbox_Security_System#Startup_Security.2C_Take_Two |title=17 Mistakes Microsoft Made in the Xbox Security System |author=Michael Steil ] TEA is also susceptible to a related-key attack which requires 2²³ chosen plaintexts under a related-key pair, with 2³² time complexity.cite journal | first = John | last = Kelsey | coauthors = Schneier, Bruce; Wagner, David | title = Related-key cryptanalysis of 3-WAY, Biham-DES, CAST, DES-X NewDES, RC2, and TEA | url = http://citeseer.ist.psu.edu/318172.html
journal = Lecture Notes in Computer Science | volume = 1334 | pages = 233–246 | date = 1997 | doi = 10.1007/BFb0028479] Because of these weaknesses, a number of revisions of TEA have been designed.

The unusually small size of the TEA algorithm would make it a viable option in situations where there are extreme constraints, e.g., legacy hardware systems (perhaps embedded) where the amount of available RAM is minimal.

Versions

The first published version of TEA was supplemented by a second version that incorporated extensions to make it more secure. "Block TEA" (sometimes referred to as XTEA) operates on arbitrary-size blocks in place of the 64-bit blocks of the original.

A third version (XXTEA), published in 1998, described further improvements for enhancing the security of the Block TEA algorithm.

Reference code

Following is an adaptation of the reference encryption and decryption routines in C, released into the public domain by David Wheeler and Roger Needham:

#include

void encrypt (uint32_t* v, uint32_t* k) { uint32_t v0=v [0] , v1=v [1] , sum=0, i; /* set up */ uint32_t delta=0x9e3779b9; /* a key schedule constant */ uint32_t k0=k [0] , k1=k [1] , k2=k [2] , k3=k [3] ; /* cache key */ for (i=0; i < 32; i++) { /* basic cycle start */ sum += delta; v0 += ((v1<<4) + k0) ^ (v1 + sum) ^ ((v1>>5) + k1); v1 += ((v0<<4) + k2) ^ (v0 + sum) ^ ((v0>>5) + k3); } /* end cycle */ v [0] =v0; v [1] =v1;}

void decrypt (uint32_t* v, uint32_t* k) { uint32_t v0=v [0] , v1=v [1] , sum=0xC6EF3720, i; /* set up */ uint32_t delta=0x9e3779b9; /* a key schedule constant */ uint32_t k0=k [0] , k1=k [1] , k2=k [2] , k3=k [3] ; /* cache key */ for (i=0; i<32; i++) { /* basic cycle start */ v1 -= ((v0<<4) + k2) ^ (v0 + sum) ^ ((v0>>5) + k3); v0 -= ((v1<<4) + k0) ^ (v1 + sum) ^ ((v1>>5) + k1); sum -= delta; } /* end cycle */ v [0] =v0; v [1] =v1;}

Note that the reference implementation is bound to specific microprocessor architecture meaning that byte order considerations are important when cyphertext is shared and processed on different systems. The original paper does not specify any details about microprocessor architecture and so anyone implementing a system using TEA would need to make those specifications for themselves.

ee also

* RC4 - A stream cipher that, just like TEA, is designed to be very simple to implement.
* XTEA - First version of Block TEA's successor.
* XXTEA - Corrected Block TEA's successor.

References

Other References

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External links

* [http://www.cs.ua.edu/SecurityResearchGroup/VRAndem.pdf A Cryptanalysis of the Tiny Encryption Algorithm]
* [http://143.53.36.235:8080/tea.htm A web page advocating TEA and providing a variety of implementations]
** [http://www.babelfish.nl/?view=actFlaw A note on the JavaScript implementations at that site]
* [http://www.cix.co.uk/~klockstone/teavect.htm Test vectors for TEA]
* [http://www-users.cs.york.ac.uk/~matthew/TEA/TEA.html A survey of TEA and XTEA and their cryptanalysis]
* [http://www.farfarfar.com/scripts/encrypt/ JavaScript implementation of XXTEA with Base64]
* [http://www.php-einfach.de/sonstiges_generator_xtea.php PHP implementation of XTEA]
* [http://www.movable-type.co.uk/scripts/TEA.html JavaScript implementation of TEA]
* [http://www.babelfish.nl/?view=actTEA JavaScript and PHP implementations of XTEA (English text)]
* [http://www.coolcode.cn/?p=128 JavaScript and PHP implementation of XXTEA]
* [http://www.jools.net/projects/ruby/crypto/ Ruby implementation of XXTEA with Base64]
* [http://www.winterwell.com/software/TEA.php LGPL Java/J2ME implementation of TEA]