ring/ec/curve25519/ed25519/
signing.rs

1// Copyright 2015-2016 Brian Smith.
2//
3// Permission to use, copy, modify, and/or distribute this software for any
4// purpose with or without fee is hereby granted, provided that the above
5// copyright notice and this permission notice appear in all copies.
6//
7// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
8// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
10// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
14
15//! EdDSA Signatures.
16
17use super::{super::ops::*, eddsa_digest, ED25519_PUBLIC_KEY_LEN};
18use crate::{
19    cpu, digest, error,
20    io::der,
21    pkcs8, rand,
22    signature::{self, KeyPair as SigningKeyPair},
23};
24
25/// An Ed25519 key pair, for signing.
26pub struct Ed25519KeyPair {
27    // RFC 8032 Section 5.1.6 calls this *s*.
28    private_scalar: Scalar,
29
30    // RFC 8032 Section 5.1.6 calls this *prefix*.
31    private_prefix: Prefix,
32
33    // RFC 8032 Section 5.1.5 calls this *A*.
34    public_key: PublicKey,
35}
36
37derive_debug_via_field!(Ed25519KeyPair, stringify!(Ed25519KeyPair), public_key);
38
39impl Ed25519KeyPair {
40    /// Generates a new key pair and returns the key pair serialized as a
41    /// PKCS#8 document.
42    ///
43    /// The PKCS#8 document will be a v2 `OneAsymmetricKey` with the public key,
44    /// as described in [RFC 5958 Section 2]; see [RFC 8410 Section 10.3] for an
45    /// example.
46    ///
47    /// [RFC 5958 Section 2]: https://tools.ietf.org/html/rfc5958#section-2
48    /// [RFC 8410 Section 10.3]: https://tools.ietf.org/html/rfc8410#section-10.3
49    pub fn generate_pkcs8(
50        rng: &dyn rand::SecureRandom,
51    ) -> Result<pkcs8::Document, error::Unspecified> {
52        let seed: [u8; SEED_LEN] = rand::generate(rng)?.expose();
53        let key_pair = Self::from_seed_(&seed);
54        Ok(pkcs8::wrap_key(
55            &PKCS8_TEMPLATE,
56            &seed[..],
57            key_pair.public_key().as_ref(),
58        ))
59    }
60
61    /// Constructs an Ed25519 key pair by parsing an unencrypted PKCS#8 v2
62    /// Ed25519 private key.
63    ///
64    /// `openssl genpkey -algorithm ED25519` generates PKCS# v1 keys, which
65    /// require the use of `Ed25519KeyPair::from_pkcs8_maybe_unchecked()`
66    /// instead of `Ed25519KeyPair::from_pkcs8()`.
67    ///
68    /// The input must be in PKCS#8 v2 format, and in particular it must contain
69    /// the public key in addition to the private key. `from_pkcs8()` will
70    /// verify that the public key and the private key are consistent with each
71    /// other.
72    ///
73    /// Some early implementations of PKCS#8 v2, including earlier versions of
74    /// *ring* and other implementations, wrapped the public key in the wrong
75    /// ASN.1 tags. Both that incorrect form and the standardized form are
76    /// accepted.
77    ///
78    /// If you need to parse PKCS#8 v1 files (without the public key) then use
79    /// `Ed25519KeyPair::from_pkcs8_maybe_unchecked()` instead.
80    pub fn from_pkcs8(pkcs8: &[u8]) -> Result<Self, error::KeyRejected> {
81        let version = pkcs8::Version::V2Only(pkcs8::PublicKeyOptions {
82            accept_legacy_ed25519_public_key_tag: true,
83        });
84        let (seed, public_key) = unwrap_pkcs8(version, untrusted::Input::from(pkcs8))?;
85        Self::from_seed_and_public_key(
86            seed.as_slice_less_safe(),
87            public_key.unwrap().as_slice_less_safe(),
88        )
89    }
90
91    /// Constructs an Ed25519 key pair by parsing an unencrypted PKCS#8 v1 or v2
92    /// Ed25519 private key.
93    ///
94    /// `openssl genpkey -algorithm ED25519` generates PKCS# v1 keys.
95    ///
96    /// It is recommended to use `Ed25519KeyPair::from_pkcs8()`, which accepts
97    /// only PKCS#8 v2 files that contain the public key.
98    /// `from_pkcs8_maybe_unchecked()` parses PKCS#2 files exactly like
99    /// `from_pkcs8()`. It also accepts v1 files. PKCS#8 v1 files do not contain
100    /// the public key, so when a v1 file is parsed the public key will be
101    /// computed from the private key, and there will be no consistency check
102    /// between the public key and the private key.
103    ///
104    /// Some early implementations of PKCS#8 v2, including earlier versions of
105    /// *ring* and other implementations, wrapped the public key in the wrong
106    /// ASN.1 tags. Both that incorrect form and the standardized form are
107    /// accepted.
108    ///
109    /// PKCS#8 v2 files are parsed exactly like `Ed25519KeyPair::from_pkcs8()`.
110    pub fn from_pkcs8_maybe_unchecked(pkcs8: &[u8]) -> Result<Self, error::KeyRejected> {
111        let version = pkcs8::Version::V1OrV2(pkcs8::PublicKeyOptions {
112            accept_legacy_ed25519_public_key_tag: true,
113        });
114        let (seed, public_key) = unwrap_pkcs8(version, untrusted::Input::from(pkcs8))?;
115        if let Some(public_key) = public_key {
116            Self::from_seed_and_public_key(
117                seed.as_slice_less_safe(),
118                public_key.as_slice_less_safe(),
119            )
120        } else {
121            Self::from_seed_unchecked(seed.as_slice_less_safe())
122        }
123    }
124
125    /// Constructs an Ed25519 key pair from the private key seed `seed` and its
126    /// public key `public_key`.
127    ///
128    /// It is recommended to use `Ed25519KeyPair::from_pkcs8()` instead.
129    ///
130    /// The private and public keys will be verified to be consistent with each
131    /// other. This helps avoid misuse of the key (e.g. accidentally swapping
132    /// the private key and public key, or using the wrong private key for the
133    /// public key). This also detects any corruption of the public or private
134    /// key.
135    pub fn from_seed_and_public_key(
136        seed: &[u8],
137        public_key: &[u8],
138    ) -> Result<Self, error::KeyRejected> {
139        let pair = Self::from_seed_unchecked(seed)?;
140
141        // This implicitly verifies that `public_key` is the right length.
142        // XXX: This rejects ~18 keys when they are partially reduced, though
143        // those keys are virtually impossible to find.
144        if public_key != pair.public_key.as_ref() {
145            let err = if public_key.len() != pair.public_key.as_ref().len() {
146                error::KeyRejected::invalid_encoding()
147            } else {
148                error::KeyRejected::inconsistent_components()
149            };
150            return Err(err);
151        }
152
153        Ok(pair)
154    }
155
156    /// Constructs a Ed25519 key pair from the private key seed `seed`.
157    ///
158    /// It is recommended to use `Ed25519KeyPair::from_pkcs8()` instead. When
159    /// that is not practical, it is recommended to use
160    /// `Ed25519KeyPair::from_seed_and_public_key()` instead.
161    ///
162    /// Since the public key is not given, the public key will be computed from
163    /// the private key. It is not possible to detect misuse or corruption of
164    /// the private key since the public key isn't given as input.
165    pub fn from_seed_unchecked(seed: &[u8]) -> Result<Self, error::KeyRejected> {
166        let seed = seed
167            .try_into()
168            .map_err(|_| error::KeyRejected::invalid_encoding())?;
169        Ok(Self::from_seed_(seed))
170    }
171
172    fn from_seed_(seed: &Seed) -> Self {
173        let h = digest::digest(&digest::SHA512, seed);
174        let (private_scalar, private_prefix) = h.as_ref().split_at(SCALAR_LEN);
175
176        let private_scalar =
177            MaskedScalar::from_bytes_masked(private_scalar.try_into().unwrap()).into();
178
179        let a = ExtPoint::from_scalarmult_base_consttime(&private_scalar, cpu::features());
180
181        Self {
182            private_scalar,
183            private_prefix: private_prefix.try_into().unwrap(),
184            public_key: PublicKey(a.into_encoded_point()),
185        }
186    }
187
188    /// Returns the signature of the message `msg`.
189    pub fn sign(&self, msg: &[u8]) -> signature::Signature {
190        signature::Signature::new(|signature_bytes| {
191            prefixed_extern! {
192                fn x25519_sc_muladd(
193                    s: &mut [u8; SCALAR_LEN],
194                    a: &Scalar,
195                    b: &Scalar,
196                    c: &Scalar,
197                );
198            }
199
200            let (signature_bytes, _unused) = signature_bytes.split_at_mut(ELEM_LEN + SCALAR_LEN);
201            let (signature_r, signature_s) = signature_bytes.split_at_mut(ELEM_LEN);
202            let nonce = {
203                let mut ctx = digest::Context::new(&digest::SHA512);
204                ctx.update(&self.private_prefix);
205                ctx.update(msg);
206                ctx.finish()
207            };
208            let nonce = Scalar::from_sha512_digest_reduced(nonce);
209
210            let r = ExtPoint::from_scalarmult_base_consttime(&nonce, cpu::features());
211            signature_r.copy_from_slice(&r.into_encoded_point());
212            let hram_digest = eddsa_digest(signature_r, self.public_key.as_ref(), msg);
213            let hram = Scalar::from_sha512_digest_reduced(hram_digest);
214            unsafe {
215                x25519_sc_muladd(
216                    signature_s.try_into().unwrap(),
217                    &hram,
218                    &self.private_scalar,
219                    &nonce,
220                );
221            }
222
223            SIGNATURE_LEN
224        })
225    }
226}
227
228impl signature::KeyPair for Ed25519KeyPair {
229    type PublicKey = PublicKey;
230
231    fn public_key(&self) -> &Self::PublicKey {
232        &self.public_key
233    }
234}
235
236#[derive(Clone, Copy)]
237pub struct PublicKey([u8; ED25519_PUBLIC_KEY_LEN]);
238
239impl AsRef<[u8]> for PublicKey {
240    fn as_ref(&self) -> &[u8] {
241        self.0.as_ref()
242    }
243}
244
245derive_debug_self_as_ref_hex_bytes!(PublicKey);
246
247fn unwrap_pkcs8(
248    version: pkcs8::Version,
249    input: untrusted::Input,
250) -> Result<(untrusted::Input, Option<untrusted::Input>), error::KeyRejected> {
251    let (private_key, public_key) = pkcs8::unwrap_key(&PKCS8_TEMPLATE, version, input)?;
252    let private_key = private_key
253        .read_all(error::Unspecified, |input| {
254            der::expect_tag_and_get_value(input, der::Tag::OctetString)
255        })
256        .map_err(|error::Unspecified| error::KeyRejected::invalid_encoding())?;
257    Ok((private_key, public_key))
258}
259
260type Prefix = [u8; PREFIX_LEN];
261const PREFIX_LEN: usize = digest::SHA512_OUTPUT_LEN - SCALAR_LEN;
262
263const SIGNATURE_LEN: usize = ELEM_LEN + SCALAR_LEN;
264
265type Seed = [u8; SEED_LEN];
266const SEED_LEN: usize = 32;
267
268static PKCS8_TEMPLATE: pkcs8::Template = pkcs8::Template {
269    bytes: include_bytes!("ed25519_pkcs8_v2_template.der"),
270    alg_id_range: core::ops::Range { start: 7, end: 12 },
271    curve_id_index: 0,
272    private_key_index: 0x10,
273};
ring/ec/curve25519/ed25519/signing.rs

ring/ec/curve25519/ed25519/
signing.rs
