crashtest-r0ket/firmware/basic/xxtea.c

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/* simple XXTEA en/decrypt utility
*
* BSD Licence
*
* btea function is from
* <https://secure.wikimedia.org/wikipedia/en/wiki/XXTEA#Reference_code>
*
* (c) by Sec <sec@42.org> 6/2011
*/
#include <stdint.h>
#define DELTA 0x9e3779b9
#define MX (((z>>5^y<<2) + (y>>3^z<<4)) ^ ((sum^y) + (k[(p&3)^e] ^ z)))
#include "xxtea.h"
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void xxtea_encode_words(uint32_t *v, int n, uint32_t const k[4])
{
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if(k[0] == 0 && k[1] == 0 && k[2] == 0 && k[3] == 0) return;
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uint32_t y, z, sum;
unsigned p, rounds, e;
rounds = 6 + 52/n;
sum = 0;
z = v[n-1];
do {
sum += DELTA;
e = (sum >> 2) & 3;
for (p=0; p<n-1; p++) {
y = v[p+1];
z = v[p] += MX;
}
y = v[0];
z = v[n-1] += MX;
} while (--rounds);
}
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void xxtea_decode_words(uint32_t *v, int n, uint32_t const k[4])
{
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if(k[0] == 0 && k[1] == 0 && k[2] == 0 && k[3] == 0) return;
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uint32_t y, z, sum;
unsigned p, rounds, e;
rounds = 6 + 52/n;
sum = rounds*DELTA;
y = v[0];
do {
e = (sum >> 2) & 3;
for (p=n-1; p>0; p--) {
z = v[p-1];
y = v[p] -= MX;
}
z = v[n-1];
y = v[0] -= MX;
} while ((sum -= DELTA) != 0);
}