diff --git a/Userland/Libraries/LibCrypto/Padding/OAEP.h b/Userland/Libraries/LibCrypto/Padding/OAEP.h index 6c329705c98..2f15e7cf7ab 100644 --- a/Userland/Libraries/LibCrypto/Padding/OAEP.h +++ b/Userland/Libraries/LibCrypto/Padding/OAEP.h @@ -73,6 +73,67 @@ public: // 12. Output EM. return em; } + + // https://www.rfc-editor.org/rfc/rfc3447#section-7.1.1 + template + static ErrorOr eme_encode(ReadonlyBytes message, ReadonlyBytes label, u32 rsa_modulus_n, Function seed_function = fill_with_random) + { + // FIXME: 1. If the length of L is greater than the input limitation for the + // hash function (2^61 - 1 octets for SHA-1), output "label too + // long" and stop. + + // 2. If mLen > k - 2hLen - 2, output "message too long" and stop. + auto m_len = message.size(); + auto k = rsa_modulus_n; + auto h_len = HashFunction::digest_size(); + auto max_message_size = k - (2 * h_len) - 2; + if (m_len > max_message_size) + return Error::from_string_view("message too long"sv); + + // 3. If the label L is not provided, let L be the empty string. Let lHash = Hash(L), an octet string of length hLen. + HashFunction hash; + hash.update(label); + auto digest = hash.digest(); + auto l_hash = digest.bytes(); + + // 4. Generate an octet string PS consisting of k - mLen - 2hLen - 2 zero octets. The length of PS may be zero. + auto ps_size = k - m_len - (2 * h_len) - 2; + auto ps = TRY(ByteBuffer::create_zeroed(ps_size)); + + // 5. Concatenate lHash, PS, a single octet with hexadecimal value 0x01, and the message M + // to form a data block DB of length k - hLen - 1 octets as DB = lHash || PS || 0x01 || M. + auto db = TRY(ByteBuffer::create_uninitialized(0)); + TRY(db.try_append(l_hash)); + TRY(db.try_append(ps.bytes())); + TRY(db.try_append(0x01)); + TRY(db.try_append(message)); + + // 6. Generate a random octet string seed of length hLen. + auto seed = TRY(ByteBuffer::create_uninitialized(h_len)); + seed_function(seed); + + // 7. Let dbMask = MGF(seed, k - hLen - 1). + auto db_mask = TRY(MaskGenerationFunction::template mgf1(seed, k - h_len - 1)); + + // 8. Let maskedDB = DB \xor dbMask. + auto masked_db = TRY(ByteBuffer::xor_buffers(db, db_mask)); + + // 9. Let seedMask = MGF(maskedDB, hLen). + auto seed_mask = TRY(MaskGenerationFunction::template mgf1(masked_db, h_len)); + + // 10. Let maskedSeed = seed \xor seedMask. + auto masked_seed = TRY(ByteBuffer::xor_buffers(seed, seed_mask)); + + // 11. Concatenate a single octet with hexadecimal value 0x00, maskedSeed, and maskedDB + // to form an encoded message EM of length k octets as EM = 0x00 || maskedSeed || maskedDB. + auto em = TRY(ByteBuffer::create_uninitialized(0)); + TRY(em.try_append(0x00)); + TRY(em.try_append(masked_seed)); + TRY(em.try_append(masked_db)); + + // 12. Output EM. + return em; + } }; }