ed448.h
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/*
* Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved.
* Copyright 2015-2016 Cryptography Research, Inc.
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*
* Originally written by Mike Hamburg
*/
#ifndef HEADER_ED448_H
# define HEADER_ED448_H
# include "point_448.h"
/* Number of bytes in an EdDSA public key. */
# define EDDSA_448_PUBLIC_BYTES 57
/* Number of bytes in an EdDSA private key. */
# define EDDSA_448_PRIVATE_BYTES EDDSA_448_PUBLIC_BYTES
/* Number of bytes in an EdDSA private key. */
# define EDDSA_448_SIGNATURE_BYTES (EDDSA_448_PUBLIC_BYTES + \
EDDSA_448_PRIVATE_BYTES)
/* EdDSA encoding ratio. */
# define C448_EDDSA_ENCODE_RATIO 4
/* EdDSA decoding ratio. */
# define C448_EDDSA_DECODE_RATIO (4 / 4)
/*
* EdDSA key generation. This function uses a different (non-Decaf) encoding.
*
* pubkey (out): The public key.
* privkey (in): The private key.
*/
c448_error_t c448_ed448_derive_public_key(
uint8_t pubkey [EDDSA_448_PUBLIC_BYTES],
const uint8_t privkey [EDDSA_448_PRIVATE_BYTES]);
/*
* EdDSA signing.
*
* signature (out): The signature.
* privkey (in): The private key.
* pubkey (in): The public key.
* message (in): The message to sign.
* message_len (in): The length of the message.
* prehashed (in): Nonzero if the message is actually the hash of something
* you want to sign.
* context (in): A "context" for this signature of up to 255 bytes.
* context_len (in): Length of the context.
*
* For Ed25519, it is unsafe to use the same key for both prehashed and
* non-prehashed messages, at least without some very careful protocol-level
* disambiguation. For Ed448 it is safe.
*/
c448_error_t c448_ed448_sign(
uint8_t signature[EDDSA_448_SIGNATURE_BYTES],
const uint8_t privkey[EDDSA_448_PRIVATE_BYTES],
const uint8_t pubkey[EDDSA_448_PUBLIC_BYTES],
const uint8_t *message, size_t message_len,
uint8_t prehashed, const uint8_t *context,
size_t context_len);
/*
* EdDSA signing with prehash.
*
* signature (out): The signature.
* privkey (in): The private key.
* pubkey (in): The public key.
* hash (in): The hash of the message. This object will not be modified by the
* call.
* context (in): A "context" for this signature of up to 255 bytes. Must be the
* same as what was used for the prehash.
* context_len (in): Length of the context.
*
* For Ed25519, it is unsafe to use the same key for both prehashed and
* non-prehashed messages, at least without some very careful protocol-level
* disambiguation. For Ed448 it is safe.
*/
c448_error_t c448_ed448_sign_prehash(
uint8_t signature[EDDSA_448_SIGNATURE_BYTES],
const uint8_t privkey[EDDSA_448_PRIVATE_BYTES],
const uint8_t pubkey[EDDSA_448_PUBLIC_BYTES],
const uint8_t hash[64],
const uint8_t *context,
size_t context_len);
/*
* EdDSA signature verification.
*
* Uses the standard (i.e. less-strict) verification formula.
*
* signature (in): The signature.
* pubkey (in): The public key.
* message (in): The message to verify.
* message_len (in): The length of the message.
* prehashed (in): Nonzero if the message is actually the hash of something you
* want to verify.
* context (in): A "context" for this signature of up to 255 bytes.
* context_len (in): Length of the context.
*
* For Ed25519, it is unsafe to use the same key for both prehashed and
* non-prehashed messages, at least without some very careful protocol-level
* disambiguation. For Ed448 it is safe.
*/
c448_error_t c448_ed448_verify(const uint8_t
signature[EDDSA_448_SIGNATURE_BYTES],
const uint8_t
pubkey[EDDSA_448_PUBLIC_BYTES],
const uint8_t *message, size_t message_len,
uint8_t prehashed, const uint8_t *context,
uint8_t context_len);
/*
* EdDSA signature verification.
*
* Uses the standard (i.e. less-strict) verification formula.
*
* signature (in): The signature.
* pubkey (in): The public key.
* hash (in): The hash of the message. This object will not be modified by the
* call.
* context (in): A "context" for this signature of up to 255 bytes. Must be the
* same as what was used for the prehash.
* context_len (in): Length of the context.
*
* For Ed25519, it is unsafe to use the same key for both prehashed and
* non-prehashed messages, at least without some very careful protocol-level
* disambiguation. For Ed448 it is safe.
*/
c448_error_t c448_ed448_verify_prehash(
const uint8_t signature[EDDSA_448_SIGNATURE_BYTES],
const uint8_t pubkey[EDDSA_448_PUBLIC_BYTES],
const uint8_t hash[64],
const uint8_t *context,
uint8_t context_len);
/*
* EdDSA point encoding. Used internally, exposed externally.
* Multiplies by C448_EDDSA_ENCODE_RATIO first.
*
* The multiplication is required because the EdDSA encoding represents
* the cofactor information, but the Decaf encoding ignores it (which
* is the whole point). So if you decode from EdDSA and re-encode to
* EdDSA, the cofactor info must get cleared, because the intermediate
* representation doesn't track it.
*
* The way we handle this is to multiply by C448_EDDSA_DECODE_RATIO when
* decoding, and by C448_EDDSA_ENCODE_RATIO when encoding. The product of
* these ratios is always exactly the cofactor 4, so the cofactor ends up
* cleared one way or another. But exactly how that shakes out depends on the
* base points specified in RFC 8032.
*
* The upshot is that if you pass the Decaf/Ristretto base point to
* this function, you will get C448_EDDSA_ENCODE_RATIO times the
* EdDSA base point.
*
* enc (out): The encoded point.
* p (in): The point.
*/
void curve448_point_mul_by_ratio_and_encode_like_eddsa(
uint8_t enc [EDDSA_448_PUBLIC_BYTES],
const curve448_point_t p);
/*
* EdDSA point decoding. Multiplies by C448_EDDSA_DECODE_RATIO, and
* ignores cofactor information.
*
* See notes on curve448_point_mul_by_ratio_and_encode_like_eddsa
*
* enc (out): The encoded point.
* p (in): The point.
*/
c448_error_t curve448_point_decode_like_eddsa_and_mul_by_ratio(
curve448_point_t p,
const uint8_t enc[EDDSA_448_PUBLIC_BYTES]);
/*
* EdDSA to ECDH private key conversion
* Using the appropriate hash function, hash the EdDSA private key
* and keep only the lower bytes to get the ECDH private key
*
* x (out): The ECDH private key as in RFC7748
* ed (in): The EdDSA private key
*/
c448_error_t c448_ed448_convert_private_key_to_x448(
uint8_t x[X448_PRIVATE_BYTES],
const uint8_t ed[EDDSA_448_PRIVATE_BYTES]);
#endif /* HEADER_ED448_H */