Tiny Encryption Algorithm

Source: Wikipedia, the free encyclopedia.
This article is about the Tiny Encryption Algorithm. It is not to be confused with the
TETRA encryption algorithm
.

TEA
chosen plaintexts and a time complexity of 232.[2] The best structural cryptanalysis of TEA in the standard single secret key setting is the zero-correlation cryptanalysis breaking 21 rounds in 2121.5 time with less than the full code book [3]

In

Fast Software Encryption workshop in Leuven in 1994, and first published in the proceedings of that workshop.[4]

The cipher is not subject to any patents.

Properties

TEA operates on two 32-bit

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 0x9E3779B9 is chosen to be ⌊232⁄𝜙⌋, where 𝜙 is the golden ratio (as a nothing-up-my-sleeve number).[4]

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

chosen plaintexts under a related-key pair, with 232 time complexity.[2] Because of these weaknesses, the XTEA
cipher was designed.

Versions

The first published version of TEA was supplemented by a second version that incorporated extensions to make it more secure. Block TEA (which was specified along with 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:[4] 

#include <stdint.h>

void encrypt (uint32_t v[2], const uint32_t k[4]) {
    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[2], const uint32_t k[4]) {
    uint32_t v0=v[0], v1=v[1], sum=0xC6EF3720, i;  /* set up; sum is (delta << 5) & 0xFFFFFFFF */
    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 acts on multi-byte numeric values. The original paper does not specify how to derive the numbers it acts on from binary or other content.

See 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.
  • Treyfer – A simple and compact encryption algorithm with 64-bit key size and block size.

Notes

  1. ^ Matthew D. Russell (27 February 2004). "Tinyness: An Overview of TEA and Related Ciphers". Archived from the original on 12 August 2007.
  2. ^
    ISBN 978-3-540-63696-0
    .
  3. ISBN 978-3-642-34046-8
    .
  4. ^
    ISBN 978-3-540-60590-4.{{cite book}}: CS1 maint: location missing publisher (link
    )
  5. ISBN 978-3-540-61512-5. Archived from the original
    (PDF) on 8 February 2012. Retrieved 25 February 2008.
  6. ^ Michael Steil. "17 Mistakes Microsoft Made in the Xbox Security System". Archived from the original on 16 April 2009.

References

External links
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