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78 lines
2.9 KiB
C++
78 lines
2.9 KiB
C++
/*
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* Copyright (c) 2024, stelar7 <dudedbz@gmail.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/ByteBuffer.h>
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#include <AK/ByteReader.h>
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#include <AK/Endian.h>
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#include <AK/Function.h>
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#include <AK/Random.h>
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#include <LibCrypto/BigInt/UnsignedBigInteger.h>
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namespace Crypto::Padding {
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// https://datatracker.ietf.org/doc/html/rfc2437#section-9.1.1
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class OAEP {
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public:
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// https://datatracker.ietf.org/doc/html/rfc2437#section-9.1.1.1
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template<typename HashFunction, typename MaskGenerationFunction>
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static ErrorOr<ByteBuffer> encode(ReadonlyBytes message, ReadonlyBytes parameters, size_t length, Function<void(Bytes)> seed_function = fill_with_random)
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{
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// FIXME: 1. If the length of P is greater than the input limitation for the
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// hash function (2^61-1 octets for SHA-1) then output "parameter string
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// too long" and stop.
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// 2. If ||M|| > emLen - 2hLen - 1 then output "message too long" and stop.
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auto h_len = HashFunction::digest_size();
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auto max_message_size = length - (2 * h_len) - 1;
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if (message.size() > max_message_size)
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return Error::from_string_view("message too long"sv);
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// 3. Generate an octet string PS consisting of emLen-||M||-2hLen-1 zero octets. The length of PS may be 0.
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auto padding_size = length - message.size() - (2 * h_len) - 1;
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auto ps = TRY(ByteBuffer::create_zeroed(padding_size));
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// 4. Let pHash = Hash(P), an octet string of length hLen.
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HashFunction hash;
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hash.update(parameters);
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auto digest = hash.digest();
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auto p_hash = digest.bytes();
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// 5. Concatenate pHash, PS, the message M, and other padding to form a data block DB as: DB = pHash || PS || 01 || M
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auto db = TRY(ByteBuffer::create_uninitialized(0));
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TRY(db.try_append(p_hash));
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TRY(db.try_append(ps.bytes()));
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TRY(db.try_append(0x01));
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TRY(db.try_append(message));
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// 6. Generate a random octet string seed of length hLen.
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auto seed = TRY(ByteBuffer::create_uninitialized(h_len));
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seed_function(seed);
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// 7. Let dbMask = MGF(seed, emLen-hLen).
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auto db_mask = TRY(MaskGenerationFunction::template mgf1<HashFunction>(seed, length - h_len));
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// 8. Let maskedDB = DB \xor dbMask.
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auto masked_db = TRY(ByteBuffer::xor_buffers(db, db_mask));
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// 9. Let seedMask = MGF(maskedDB, hLen).
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auto seed_mask = TRY(MaskGenerationFunction::template mgf1<HashFunction>(masked_db, h_len));
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// 10. Let maskedSeed = seed \xor seedMask.
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auto masked_seed = TRY(ByteBuffer::xor_buffers(seed, seed_mask));
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// 11. Let EM = maskedSeed || maskedDB.
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auto em = TRY(ByteBuffer::create_uninitialized(0));
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TRY(em.try_append(masked_seed));
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TRY(em.try_append(masked_db));
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// 12. Output EM.
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return em;
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}
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};
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}
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