c2pa_crypto/raw_signature/
validator.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
// Copyright 2024 Adobe. All rights reserved.
// This file is licensed to you under the Apache License,
// Version 2.0 (http://www.apache.org/licenses/LICENSE-2.0)
// or the MIT license (http://opensource.org/licenses/MIT),
// at your option.

// Unless required by applicable law or agreed to in writing,
// this software is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR REPRESENTATIONS OF ANY KIND, either express or
// implied. See the LICENSE-MIT and LICENSE-APACHE files for the
// specific language governing permissions and limitations under
// each license.

use async_trait::async_trait;
use bcder::Oid;
use thiserror::Error;

use crate::raw_signature::{oids::*, SigningAlg};

/// A `RawSignatureValidator` implementation checks a signature encoded using a
/// specific signature algorithm and a private/public key pair.
///
/// IMPORTANT: This signature is typically embedded in a wrapper provided by
/// another signature mechanism. In the C2PA ecosystem, this wrapper is
/// typically COSE, but `RawSignatureValidator` does not implement COSE.
pub trait RawSignatureValidator {
    /// Return `Ok(())` if the signature `sig` is valid for the raw content
    /// `data` and the public key `public_key`.
    fn validate(
        &self,
        sig: &[u8],
        data: &[u8],
        public_key: &[u8],
    ) -> Result<(), RawSignatureValidationError>;
}

/// An `AsyncRawSignatureValidator` implementation checks a signature encoded
/// using a specific signature algorithm and a private/public key pair.
///
/// IMPORTANT: This signature is typically embedded in a wrapper provided by
/// another signature mechanism. In the C2PA ecosystem, this wrapper is
/// typically COSE, but `AsyncRawSignatureValidator` does not implement COSE.
///
/// The WASM implementation of `c2pa-crypto` also implements
/// [`RawSignatureValidator`] (the synchronous version), but some encryption
/// algorithms are not supported. For that reason, it's preferable to use this
/// implementation on WASM.
///
/// [`RawSignatureValidator`]: crate::raw_signature::RawSignatureValidator
#[async_trait(?Send)]
pub trait AsyncRawSignatureValidator {
    /// Return `Ok(())` if the signature `sig` is valid for the raw content
    /// `data` and the public key `public_key`.
    async fn validate_async(
        &self,
        sig: &[u8],
        data: &[u8],
        public_key: &[u8],
    ) -> Result<(), RawSignatureValidationError>;
}

/// Return a built-in signature validator for the requested signature
/// algorithm.
///
/// Which validators are available may vary depending on the platform and
/// which crate features were enabled.
pub fn validator_for_signing_alg(alg: SigningAlg) -> Option<Box<dyn RawSignatureValidator>> {
    #[cfg(any(target_arch = "wasm32", feature = "rust_native_crypto"))]
    {
        if let Some(validator) =
            crate::raw_signature::rust_native::validators::validator_for_signing_alg(alg)
        {
            return Some(validator);
        }
    }

    #[cfg(not(target_arch = "wasm32"))]
    if let Some(validator) =
        crate::raw_signature::openssl::validators::validator_for_signing_alg(alg)
    {
        return Some(validator);
    }

    #[cfg(all(target_arch = "wasm32", not(target_os = "wasi")))]
    if let Some(validator) =
        crate::raw_signature::webcrypto::validators::validator_for_signing_alg(alg)
    {
        return Some(validator);
    }

    let _ = alg; // this value will be unused in this case
    None
}

/// Return a built-in signature validator for the requested signature
/// algorithm as identified by OID.
///
/// Which validators are available may vary depending on the platform and
/// which crate features were enabled.
pub(crate) fn validator_for_sig_and_hash_algs(
    sig_alg: &Oid,
    hash_alg: &Oid,
) -> Option<Box<dyn RawSignatureValidator>> {
    if sig_alg.as_ref() == RSA_OID.as_bytes()
        || sig_alg.as_ref() == SHA256_WITH_RSAENCRYPTION_OID.as_bytes()
        || sig_alg.as_ref() == SHA384_WITH_RSAENCRYPTION_OID.as_bytes()
        || sig_alg.as_ref() == SHA512_WITH_RSAENCRYPTION_OID.as_bytes()
    {
        // TO REVIEW: Do we need any of the RSA-PSS algorithms for this use case?
        #[cfg(any(target_arch = "wasm32", feature = "rust_native_crypto"))]
        {
            if let Some(validator) =
                crate::raw_signature::rust_native::validators::validator_for_sig_and_hash_algs(
                    sig_alg, hash_alg,
                )
            {
                return Some(validator);
            }
        }

        #[cfg(not(target_arch = "wasm32"))]
        if let Some(validator) =
            crate::raw_signature::openssl::validators::validator_for_sig_and_hash_algs(
                sig_alg, hash_alg,
            )
        {
            return Some(validator);
        }
    } else if sig_alg.as_ref() == EC_PUBLICKEY_OID.as_bytes()
        || sig_alg.as_ref() == ECDSA_WITH_SHA256_OID.as_bytes()
        || sig_alg.as_ref() == ECDSA_WITH_SHA384_OID.as_bytes()
        || sig_alg.as_ref() == ECDSA_WITH_SHA512_OID.as_bytes()
    {
        if hash_alg.as_ref() == SHA256_OID.as_bytes() {
            return validator_for_signing_alg(SigningAlg::Es256);
        } else if hash_alg.as_ref() == SHA384_OID.as_bytes() {
            return validator_for_signing_alg(SigningAlg::Es384);
        } else if hash_alg.as_ref() == SHA512_OID.as_bytes() {
            return validator_for_signing_alg(SigningAlg::Es512);
        }
    } else if sig_alg.as_ref() == ED25519_OID.as_bytes() {
        return validator_for_signing_alg(SigningAlg::Ed25519);
    }

    None
}

/// Return a built-in signature validator for the requested signature
/// algorithm.
///
/// Which validators are available may vary depending on the platform and
/// which crate features were enabled.
///
/// IMPORTANT: Only available on WASM builds. There are no built-in async
/// validators for other platforms.
#[cfg(target_arch = "wasm32")]
pub fn async_validator_for_signing_alg(
    alg: SigningAlg,
) -> Option<Box<dyn AsyncRawSignatureValidator>> {
    crate::raw_signature::webcrypto::async_validator_for_signing_alg(alg)
}

/// Describes errors that can be identified when validating a raw signature.
#[derive(Debug, Eq, Error, PartialEq)]
#[non_exhaustive]
pub enum RawSignatureValidationError {
    /// The signature does not match the provided data or public key.
    #[error("the signature does not match the provided data or public key")]
    SignatureMismatch,

    /// An error was reported by the underlying cryptography implementation.
    #[error("an error was reported by the cryptography library: {0}")]
    CryptoLibraryError(String),

    /// An invalid public key was provided.
    #[error("invalid public key")]
    InvalidPublicKey,

    /// An invalid signature value was provided.
    #[error("invalid signature value")]
    InvalidSignature,

    /// The time stamp uses an unsupported signing or hash algorithm.
    #[error("signature uses an unsupported algorithm")]
    UnsupportedAlgorithm,

    /// An unexpected internal error occured while requesting the time stamp
    /// response.
    #[error("internal error ({0})")]
    InternalError(String),
}

#[cfg(not(target_arch = "wasm32"))]
impl From<openssl::error::ErrorStack> for RawSignatureValidationError {
    fn from(err: openssl::error::ErrorStack) -> Self {
        Self::CryptoLibraryError(err.to_string())
    }
}

#[cfg(not(target_arch = "wasm32"))]
impl From<crate::raw_signature::openssl::OpenSslMutexUnavailable> for RawSignatureValidationError {
    fn from(err: crate::raw_signature::openssl::OpenSslMutexUnavailable) -> Self {
        Self::InternalError(err.to_string())
    }
}

#[cfg(target_arch = "wasm32")]
impl From<crate::raw_signature::webcrypto::WasmCryptoError> for RawSignatureValidationError {
    fn from(err: crate::raw_signature::webcrypto::WasmCryptoError) -> Self {
        match err {
            crate::raw_signature::webcrypto::WasmCryptoError::UnknownContext => {
                Self::InternalError("unknown WASM context".to_string())
            }
            crate::raw_signature::webcrypto::WasmCryptoError::NoCryptoAvailable => {
                Self::InternalError("WASM crypto unavailable".to_string())
            }
        }
    }
}