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

//! SEC1 elliptic curve private key support.
//!
//! Support for ASN.1 DER-encoded elliptic curve private keys as described in
//! SEC1: Elliptic Curve Cryptography (Version 2.0) Appendix C.4 (p.108):
//!
//! <https://www.secg.org/sec1-v2.pdf>

use crate::{EcParameters, Error, Result};
use core::fmt;
use der::{
    asn1::{BitStringRef, ContextSpecific, OctetStringRef},
    Decode, DecodeValue, Encode, Header, Reader, Sequence, Tag, TagMode, TagNumber,
};

#[cfg(feature = "alloc")]
use der::SecretDocument;

#[cfg(feature = "pem")]
use der::pem::PemLabel;

/// `ECPrivateKey` version.
///
/// From [RFC5913 Section 3]:
/// > version specifies the syntax version number of the elliptic curve
/// > private key structure.  For this version of the document, it SHALL
/// > be set to ecPrivkeyVer1, which is of type INTEGER and whose value
/// > is one (1).
///
/// [RFC5915 Section 3]: https://datatracker.ietf.org/doc/html/rfc5915#section-3
const VERSION: u8 = 1;

/// Context-specific tag number for the elliptic curve parameters.
const EC_PARAMETERS_TAG: TagNumber = TagNumber::new(0);

/// Context-specific tag number for the public key.
const PUBLIC_KEY_TAG: TagNumber = TagNumber::new(1);

/// SEC1 elliptic curve private key.
///
/// Described in [SEC1: Elliptic Curve Cryptography (Version 2.0)]
/// Appendix C.4 (p.108) and also [RFC5915 Section 3]:
///
/// ```text
/// ECPrivateKey ::= SEQUENCE {
///   version        INTEGER { ecPrivkeyVer1(1) } (ecPrivkeyVer1),
///   privateKey     OCTET STRING,
///   parameters [0] ECParameters {{ NamedCurve }} OPTIONAL,
///   publicKey  [1] BIT STRING OPTIONAL
/// }
/// ```
///
/// When encoded as PEM (text), keys in this format begin with the following:
///
/// ```text
/// -----BEGIN EC PRIVATE KEY-----
/// ```
///
/// [SEC1: Elliptic Curve Cryptography (Version 2.0)]: https://www.secg.org/sec1-v2.pdf
/// [RFC5915 Section 3]: https://datatracker.ietf.org/doc/html/rfc5915#section-3
#[derive(Clone)]
#[cfg_attr(docsrs, doc(cfg(feature = "der")))]
pub struct EcPrivateKey<'a> {
    /// Private key data.
    pub private_key: &'a [u8],

    /// Elliptic curve parameters.
    pub parameters: Option<EcParameters>,

    /// Public key data, optionally available if version is V2.
    pub public_key: Option<&'a [u8]>,
}

impl<'a> DecodeValue<'a> for EcPrivateKey<'a> {
    fn decode_value<R: Reader<'a>>(reader: &mut R, header: Header) -> der::Result<Self> {
        reader.read_nested(header.length, |reader| {
            if u8::decode(reader)? != VERSION {
                return Err(der::Tag::Integer.value_error());
            }

            let private_key = OctetStringRef::decode(reader)?.as_bytes();
            let parameters = reader.context_specific(EC_PARAMETERS_TAG, TagMode::Explicit)?;
            let public_key = reader
                .context_specific::<BitStringRef<'_>>(PUBLIC_KEY_TAG, TagMode::Explicit)?
                .map(|bs| bs.as_bytes().ok_or_else(|| Tag::BitString.value_error()))
                .transpose()?;

            Ok(EcPrivateKey {
                private_key,
                parameters,
                public_key,
            })
        })
    }
}

impl<'a> Sequence<'a> for EcPrivateKey<'a> {
    fn fields<F, T>(&self, f: F) -> der::Result<T>
    where
        F: FnOnce(&[&dyn Encode]) -> der::Result<T>,
    {
        f(&[
            &VERSION,
            &OctetStringRef::new(self.private_key)?,
            &self.parameters.as_ref().map(|params| ContextSpecific {
                tag_number: EC_PARAMETERS_TAG,
                tag_mode: TagMode::Explicit,
                value: *params,
            }),
            &self
                .public_key
                .map(|pk| {
                    BitStringRef::from_bytes(pk).map(|value| ContextSpecific {
                        tag_number: PUBLIC_KEY_TAG,
                        tag_mode: TagMode::Explicit,
                        value,
                    })
                })
                .transpose()?,
        ])
    }
}

impl<'a> TryFrom<&'a [u8]> for EcPrivateKey<'a> {
    type Error = Error;

    fn try_from(bytes: &'a [u8]) -> Result<EcPrivateKey<'a>> {
        Ok(Self::from_der(bytes)?)
    }
}

impl<'a> fmt::Debug for EcPrivateKey<'a> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("EcPrivateKey")
            .field("parameters", &self.parameters)
            .field("public_key", &self.public_key)
            .finish_non_exhaustive()
    }
}

#[cfg(feature = "alloc")]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
impl TryFrom<EcPrivateKey<'_>> for SecretDocument {
    type Error = Error;

    fn try_from(private_key: EcPrivateKey<'_>) -> Result<Self> {
        SecretDocument::try_from(&private_key)
    }
}

#[cfg(feature = "alloc")]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
impl TryFrom<&EcPrivateKey<'_>> for SecretDocument {
    type Error = Error;

    fn try_from(private_key: &EcPrivateKey<'_>) -> Result<Self> {
        Ok(Self::encode_msg(private_key)?)
    }
}

#[cfg(feature = "pem")]
#[cfg_attr(docsrs, doc(cfg(feature = "pem")))]
impl PemLabel for EcPrivateKey<'_> {
    const PEM_LABEL: &'static str = "EC PRIVATE KEY";
}