2 * Copyright (c) 2018 Thomas Pornin <pornin@bolet.org>
4 * Permission is hereby granted, free of charge, to any person obtaining
5 * a copy of this software and associated documentation files (the
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12 * The above copyright notice and this permission notice shall be
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15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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21 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
28 * Hash some data. This is put as a separate function so that stack
29 * allocation of the hash function context is done only for the duration
33 hash_data(const br_hash_class *dig, void *dst, const void *src, size_t len)
35 br_hash_compat_context hc;
38 dig->init(&hc.vtable);
39 dig->update(&hc.vtable, src, len);
40 dig->out(&hc.vtable, dst);
45 br_rsa_oaep_pad(const br_prng_class **rnd, const br_hash_class *dig,
46 const void *label, size_t label_len,
47 const br_rsa_public_key *pk,
48 void *dst, size_t dst_max_len,
49 const void *src, size_t src_len)
54 hlen = br_digest_size(dig);
57 * Compute actual modulus length (in bytes).
60 while (k > 0 && pk->n[k - 1] == 0) {
65 * An error is reported if:
66 * - the modulus is too short;
67 * - the source message length is too long;
68 * - the destination buffer is too short.
70 if (k < ((hlen << 1) + 2)
71 || src_len > (k - (hlen << 1) - 2)
78 * Apply padding. At this point, things cannot fail.
83 * Assemble: DB = lHash || PS || 0x01 || M
84 * We first place the source message M with memmove(), so that
85 * overlaps between source and destination buffers are supported.
87 memmove(buf + k - src_len, src, src_len);
88 hash_data(dig, buf + 1 + hlen, label, label_len);
89 memset(buf + 1 + (hlen << 1), 0, k - src_len - (hlen << 1) - 2);
90 buf[k - src_len - 1] = 0x01;
93 * Make the random seed.
95 (*rnd)->generate(rnd, buf + 1, hlen);
98 * Mask DB with the mask generated from the seed.
100 br_mgf1_xor(buf + 1 + hlen, k - hlen - 1, dig, buf + 1, hlen);
103 * Mask the seed with the mask generated from the masked DB.
105 br_mgf1_xor(buf + 1, hlen, dig, buf + 1 + hlen, k - hlen - 1);
108 * Padding result: EM = 0x00 || maskedSeed || maskedDB.