45 lines
1.5 KiB
C
45 lines
1.5 KiB
C
#include <mbedtls/ctr_drbg.h>
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#include <mbedtls/entropy.h>
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#if defined(MBEDTLS_ENTROPY_C)
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static int
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hydro_random_init(void)
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{
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mbedtls_entropy_context entropy;
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uint16_t pos = 0;
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mbedtls_entropy_init(&entropy);
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// Pull data directly out of the entropy pool for the state, as it's small enough.
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if (mbedtls_entropy_func(&entropy, (uint8_t *) &hydro_random_context.counter,
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sizeof hydro_random_context.counter) != 0) {
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return -1;
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}
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// mbedtls_entropy_func can't provide more than MBEDTLS_ENTROPY_BLOCK_SIZE in one go.
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// This constant depends of mbedTLS configuration (whether the PRNG is backed by SHA256/SHA512
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// at this time) Therefore, if necessary, we get entropy multiple times.
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do {
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const uint8_t dataLeftToConsume = gimli_BLOCKBYTES - pos;
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const uint8_t currentChunkSize = (dataLeftToConsume > MBEDTLS_ENTROPY_BLOCK_SIZE)
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? MBEDTLS_ENTROPY_BLOCK_SIZE
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: dataLeftToConsume;
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// Forces mbedTLS to fetch fresh entropy, then get some to feed libhydrogen.
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if (mbedtls_entropy_gather(&entropy) != 0 ||
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mbedtls_entropy_func(&entropy, &hydro_random_context.state[pos], currentChunkSize) !=
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0) {
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return -1;
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}
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pos += MBEDTLS_ENTROPY_BLOCK_SIZE;
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} while (pos < gimli_BLOCKBYTES);
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mbedtls_entropy_free(&entropy);
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return 0;
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}
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#else
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#error Need an entropy source
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#endif
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