104 lines
2.5 KiB
C
104 lines
2.5 KiB
C
//
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// rng.c
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//
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// Created by Bassham, Lawrence E (Fed) on 8/29/17.
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// Copyright © 2017 Bassham, Lawrence E (Fed). All rights reserved.
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// Modified for PQClean by Sebastian Verschoor
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//
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#include "nistseedexpander.h"
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#include "aes.h"
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#include <string.h>
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/*
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seedexpander_init()
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ctx - stores the current state of an instance of the seed expander
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seed - a 32 byte random value
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diversifier - an 8 byte diversifier
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maxlen - maximum number of bytes (less than 2**32) generated under this seed and diversifier
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*/
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int
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seedexpander_init(AES_XOF_struct *ctx,
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const uint8_t *seed,
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const uint8_t *diversifier,
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size_t maxlen)
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{
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ctx->length_remaining = maxlen;
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memcpy(ctx->key, seed, 32);
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memcpy(ctx->ctr, diversifier, 8);
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ctx->ctr[11] = maxlen % 256;
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maxlen >>= 8;
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ctx->ctr[10] = maxlen % 256;
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maxlen >>= 8;
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ctx->ctr[9] = maxlen % 256;
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maxlen >>= 8;
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ctx->ctr[8] = maxlen % 256;
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memset(ctx->ctr+12, 0x00, 4);
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ctx->buffer_pos = 16;
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memset(ctx->buffer, 0x00, 16);
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return RNG_SUCCESS;
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}
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static void AES256_ECB(uint8_t *key, uint8_t *ctr, uint8_t *buffer) {
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aes256ctx ctx;
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aes256_ecb_keyexp(&ctx, key);
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aes256_ecb(buffer, ctr, 1, &ctx);
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aes256_ctx_release(&ctx);
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}
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/*
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seedexpander()
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ctx - stores the current state of an instance of the seed expander
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x - returns the XOF data
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xlen - number of bytes to return
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*/
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int
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seedexpander(AES_XOF_struct *ctx, uint8_t *x, size_t xlen)
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{
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size_t offset;
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if ( x == NULL ) {
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return RNG_BAD_OUTBUF;
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}
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if ( xlen >= ctx->length_remaining ) {
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return RNG_BAD_REQ_LEN;
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}
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ctx->length_remaining -= xlen;
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offset = 0;
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while ( xlen > 0 ) {
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if ( xlen <= (16-ctx->buffer_pos) ) { // buffer has what we need
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memcpy(x+offset, ctx->buffer+ctx->buffer_pos, xlen);
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ctx->buffer_pos += xlen;
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return RNG_SUCCESS;
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}
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// take what's in the buffer
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memcpy(x+offset, ctx->buffer+ctx->buffer_pos, 16-ctx->buffer_pos);
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xlen -= 16-ctx->buffer_pos;
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offset += 16-ctx->buffer_pos;
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AES256_ECB(ctx->key, ctx->ctr, ctx->buffer);
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ctx->buffer_pos = 0;
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//increment the counter
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for (size_t i=15; i>=12; i--) {
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if ( ctx->ctr[i] == 0xff ) {
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ctx->ctr[i] = 0x00;
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} else {
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ctx->ctr[i]++;
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break;
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}
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}
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}
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return RNG_SUCCESS;
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}
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