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Concept
XTEA
Summary
In cryptography, XTEA (eXtended TEA) is a block cipher designed to correct weaknesses in TEA. The cipher's designers were David Wheeler and Roger Needham of the Cambridge Computer Laboratory, and the algorithm was presented in an unpublished technical report in 1997 (Needham and Wheeler, 1997). It is not subject to any patents.
Like TEA, XTEA is a 64-bit block Feistel cipher with a 128-bit key and a suggested 64 rounds. Several differences from TEA are apparent, including a somewhat more complex key-schedule and a rearrangement of the shifts, XORs, and additions.
This standard C source code, adapted from the reference code released into the public domain by David Wheeler and Roger Needham, encrypts and decrypts using XTEA:
#include
/* take 64 bits of data in v[0] and v[1] and 128 bits of key[0] - key[3] /
void encipher(unsigned int num_rounds, uint32_t v[2], uint32_t const key[4]) {
unsigned int i;
uint32_t v0=v[0], v1=v[1], sum=0, delta=0x9E3779B9;
for (i=0; i < num_rounds; i++) {
v0 += (((v1 < 4) ^ (v1 >> 5)) + v1) ^ (sum + key[sum & 3]);
sum += delta;
v1 += (((v0 < 4) ^ (v0 >> 5)) + v0) ^ (sum + key[(sum>>11) & 3]);
}
v[0]=v0; v[1]=v1;
}
void decipher(unsigned int num_rounds, uint32_t v[2], uint32_t const key[4]) {
unsigned int i;
uint32_t v0=v[0], v1=v[1], delta=0x9E3779B9, sum=deltanum_rounds;
for (i=0; i < num_rounds; i++) {
v1 -= (((v0 < 4) ^ (v0 >> 5)) + v0) ^ (sum + key[(sum>>11) & 3]);
sum -= delta;
v0 -= (((v1 < 4) ^ (v1 >> 5)) + v1) ^ (sum + key[sum & 3]);
}
v[0]=v0; v[1]=v1;
}
The changes from the reference source code are minor:
The reference source code used the unsigned long type rather than the 64-bit clean uint32_t.
The reference source code did not use const types.
The reference source code omitted redundant parentheses, using C precedence to write the round function as e.g. v1 += (v0
Official source
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