xref: /openssl/crypto/ec/curve448/ed448.h (revision 3ffc6c64)
1 /*
2  * Copyright 2017-2021 The OpenSSL Project Authors. All Rights Reserved.
3  * Copyright 2015-2016 Cryptography Research, Inc.
4  *
5  * Licensed under the Apache License 2.0 (the "License").  You may not use
6  * this file except in compliance with the License.  You can obtain a copy
7  * in the file LICENSE in the source distribution or at
8  * https://www.openssl.org/source/license.html
9  *
10  * Originally written by Mike Hamburg
11  */
12 
13 #ifndef OSSL_CRYPTO_EC_CURVE448_ED448_H
14 # define OSSL_CRYPTO_EC_CURVE448_ED448_H
15 
16 # include "point_448.h"
17 
18 /* Number of bytes in an EdDSA public key. */
19 # define EDDSA_448_PUBLIC_BYTES 57
20 
21 /* Number of bytes in an EdDSA private key. */
22 # define EDDSA_448_PRIVATE_BYTES EDDSA_448_PUBLIC_BYTES
23 
24 /* Number of bytes in an EdDSA signature. */
25 # define EDDSA_448_SIGNATURE_BYTES (EDDSA_448_PUBLIC_BYTES + \
26                                     EDDSA_448_PRIVATE_BYTES)
27 
28 /* EdDSA encoding ratio. */
29 # define C448_EDDSA_ENCODE_RATIO 4
30 
31 /* EdDSA decoding ratio. */
32 # define C448_EDDSA_DECODE_RATIO (4 / 4)
33 
34 /*
35  * EdDSA key generation.  This function uses a different (non-Decaf) encoding.
36  *
37  * pubkey (out): The public key.
38  * privkey (in): The private key.
39  */
40 c448_error_t
41 ossl_c448_ed448_derive_public_key(
42                               OSSL_LIB_CTX *ctx,
43                               uint8_t pubkey [EDDSA_448_PUBLIC_BYTES],
44                               const uint8_t privkey [EDDSA_448_PRIVATE_BYTES],
45                               const char *propq);
46 
47 /*
48  * EdDSA signing.
49  *
50  * signature (out): The signature.
51  * privkey (in): The private key.
52  * pubkey (in):  The public key.
53  * message (in):  The message to sign.
54  * message_len (in):  The length of the message.
55  * prehashed (in):  Nonzero if the message is actually the hash of something
56  *                  you want to sign.
57  * context (in):  A "context" for this signature of up to 255 bytes.
58  * context_len (in):  Length of the context.
59  *
60  * For Ed25519, it is unsafe to use the same key for both prehashed and
61  * non-prehashed messages, at least without some very careful protocol-level
62  * disambiguation.  For Ed448 it is safe.
63  */
64 c448_error_t
65 ossl_c448_ed448_sign(OSSL_LIB_CTX *ctx,
66                      uint8_t signature[EDDSA_448_SIGNATURE_BYTES],
67                      const uint8_t privkey[EDDSA_448_PRIVATE_BYTES],
68                      const uint8_t pubkey[EDDSA_448_PUBLIC_BYTES],
69                      const uint8_t *message, size_t message_len,
70                      uint8_t prehashed, const uint8_t *context,
71                      size_t context_len,
72                      const char *propq);
73 
74 /*
75  * EdDSA signing with prehash.
76  *
77  * signature (out): The signature.
78  * privkey (in): The private key.
79  * pubkey (in): The public key.
80  * hash (in): The hash of the message.  This object will not be modified by the
81  *            call.
82  * context (in): A "context" for this signature of up to 255 bytes.  Must be the
83  *               same as what was used for the prehash.
84  * context_len (in): Length of the context.
85  *
86  * For Ed25519, it is unsafe to use the same key for both prehashed and
87  * non-prehashed messages, at least without some very careful protocol-level
88  * disambiguation.  For Ed448 it is safe.
89  */
90 c448_error_t
91 ossl_c448_ed448_sign_prehash(OSSL_LIB_CTX *ctx,
92                              uint8_t signature[EDDSA_448_SIGNATURE_BYTES],
93                              const uint8_t privkey[EDDSA_448_PRIVATE_BYTES],
94                              const uint8_t pubkey[EDDSA_448_PUBLIC_BYTES],
95                              const uint8_t hash[64],
96                              const uint8_t *context,
97                              size_t context_len,
98                              const char *propq);
99 
100 /*
101  * EdDSA signature verification.
102  *
103  * Uses the standard (i.e. less-strict) verification formula.
104  *
105  * signature (in): The signature.
106  * pubkey (in): The public key.
107  * message (in): The message to verify.
108  * message_len (in): The length of the message.
109  * prehashed (in): Nonzero if the message is actually the hash of something you
110  *                 want to verify.
111  * context (in): A "context" for this signature of up to 255 bytes.
112  * context_len (in): Length of the context.
113  *
114  * For Ed25519, it is unsafe to use the same key for both prehashed and
115  * non-prehashed messages, at least without some very careful protocol-level
116  * disambiguation.  For Ed448 it is safe.
117  */
118 c448_error_t
119 ossl_c448_ed448_verify(OSSL_LIB_CTX *ctx,
120                        const uint8_t
121                        signature[EDDSA_448_SIGNATURE_BYTES],
122                        const uint8_t
123                        pubkey[EDDSA_448_PUBLIC_BYTES],
124                        const uint8_t *message, size_t message_len,
125                        uint8_t prehashed, const uint8_t *context,
126                        uint8_t context_len,
127                        const char *propq);
128 
129 /*
130  * EdDSA signature verification.
131  *
132  * Uses the standard (i.e. less-strict) verification formula.
133  *
134  * signature (in): The signature.
135  * pubkey (in): The public key.
136  * hash (in): The hash of the message.  This object will not be modified by the
137  *            call.
138  * context (in): A "context" for this signature of up to 255 bytes.  Must be the
139  *               same as what was used for the prehash.
140  * context_len (in): Length of the context.
141  *
142  * For Ed25519, it is unsafe to use the same key for both prehashed and
143  * non-prehashed messages, at least without some very careful protocol-level
144  * disambiguation.  For Ed448 it is safe.
145  */
146 c448_error_t
147 ossl_c448_ed448_verify_prehash(
148                             OSSL_LIB_CTX *ctx,
149                             const uint8_t signature[EDDSA_448_SIGNATURE_BYTES],
150                             const uint8_t pubkey[EDDSA_448_PUBLIC_BYTES],
151                             const uint8_t hash[64],
152                             const uint8_t *context,
153                             uint8_t context_len,
154                             const char *propq);
155 
156 /*
157  * EdDSA point encoding.  Used internally, exposed externally.
158  * Multiplies by C448_EDDSA_ENCODE_RATIO first.
159  *
160  * The multiplication is required because the EdDSA encoding represents
161  * the cofactor information, but the Decaf encoding ignores it (which
162  * is the whole point).  So if you decode from EdDSA and re-encode to
163  * EdDSA, the cofactor info must get cleared, because the intermediate
164  * representation doesn't track it.
165  *
166  * The way we handle this is to multiply by C448_EDDSA_DECODE_RATIO when
167  * decoding, and by C448_EDDSA_ENCODE_RATIO when encoding.  The product of
168  * these ratios is always exactly the cofactor 4, so the cofactor ends up
169  * cleared one way or another.  But exactly how that shakes out depends on the
170  * base points specified in RFC 8032.
171  *
172  * The upshot is that if you pass the Decaf/Ristretto base point to
173  * this function, you will get C448_EDDSA_ENCODE_RATIO times the
174  * EdDSA base point.
175  *
176  * enc (out): The encoded point.
177  * p (in): The point.
178  */
179 void
180 ossl_curve448_point_mul_by_ratio_and_encode_like_eddsa(
181                                     uint8_t enc [EDDSA_448_PUBLIC_BYTES],
182                                     const curve448_point_t p);
183 
184 /*
185  * EdDSA point decoding.  Multiplies by C448_EDDSA_DECODE_RATIO, and
186  * ignores cofactor information.
187  *
188  * See notes on curve448_point_mul_by_ratio_and_encode_like_eddsa
189  *
190  * enc (out): The encoded point.
191  * p (in): The point.
192  */
193 c448_error_t
194 ossl_curve448_point_decode_like_eddsa_and_mul_by_ratio(
195                             curve448_point_t p,
196                             const uint8_t enc[EDDSA_448_PUBLIC_BYTES]);
197 
198 /*
199  * EdDSA to ECDH private key conversion
200  * Using the appropriate hash function, hash the EdDSA private key
201  * and keep only the lower bytes to get the ECDH private key
202  *
203  * x (out): The ECDH private key as in RFC7748
204  * ed (in): The EdDSA private key
205  */
206 c448_error_t
207 ossl_c448_ed448_convert_private_key_to_x448(
208                                     OSSL_LIB_CTX *ctx,
209                                     uint8_t x[X448_PRIVATE_BYTES],
210                                     const uint8_t ed[EDDSA_448_PRIVATE_BYTES],
211                                     const char *propq);
212 
213 #endif                          /* OSSL_CRYPTO_EC_CURVE448_ED448_H */
214