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29 * Copyright 2010 Develer S.r.l. (http://www.develer.com/)
33 * \brief ANSI X9.17 PRNG implementation
34 * \author Giovanni Bajo <rasky@develer.com>
40 #include <drv/timer.h>
41 #include "hw/hw_timer.h"
43 static void x917_next(X917Context *ctx, BlockCipher *cipher, uint8_t *out)
45 const size_t blen = cipher_block_len(cipher);
51 uint8_t padding[blen - sizeof(time_t) - sizeof(hptime_t)];
54 ASSERT(sizeof(DT) == blen);
56 memset(&DT, 0, sizeof(DT));
57 DT.t0 = timer_clock();
58 DT.t1 = timer_hw_hpread();
60 cipher_ecb_encrypt(cipher, &DT);
62 xor_block(out, (uint8_t*)&DT, ctx->state, blen);
63 cipher_ecb_encrypt(cipher, out);
65 xor_block(ctx->state, (uint8_t*)&DT, out, blen);
66 cipher_ecb_encrypt(cipher, ctx->state);
72 static void x917_generate(PRNG *ctx_, uint8_t *data, size_t len)
74 X917Context *ctx = (X917Context *)ctx_;
75 BlockCipher *cipher = AES128_stackinit();
77 const size_t blen = cipher_block_len(cipher);
81 ASSERT(sizeof(ctx->state) >= blen);
82 ASSERT(sizeof(ctx->key) >= cipher_key_len(cipher));
84 cipher_set_key(cipher, ctx->key);
88 size_t L = MIN(blen, len);
89 x917_next(ctx, cipher, temp);
90 memcpy(data, temp, L);
96 static void x917_reseed(PRNG *ctx_, const uint8_t *seed)
98 // The X9.17 standard does not specify reseeding. To avoid external
99 // dependencies, we implement it this way:
100 // * Generate a new random block, xor it with the first part
101 // of the seed, and use the result as new seed.
102 // * Generate and throw away a block to update the state.
103 X917Context *ctx = (X917Context *)ctx_;
104 const size_t klen = sizeof(ctx->key);
105 const size_t blen = sizeof(ctx->state);
107 if (!ctx->rng.seeded)
109 memcpy(ctx->key, seed, klen);
110 memcpy(ctx->state, seed+klen, blen);
115 x917_generate(ctx_, buf, klen);
117 xor_block(ctx->key, buf, seed, klen);
118 xor_block(ctx->state, ctx->state, seed+klen, blen);
124 /*********************************************************************/
126 void x917_init(X917Context *ctx)
128 ctx->rng.reseed = x917_reseed;
129 ctx->rng.generate = x917_generate;
130 ctx->rng.seed_len = sizeof(ctx->key) + sizeof(ctx->state);