aws_sigv4/sign/
v4a.rs

1/*
2 * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
3 * SPDX-License-Identifier: Apache-2.0
4 */
5
6use aws_smithy_runtime_api::client::identity::Identity;
7use bytes::{BufMut, BytesMut};
8use crypto_bigint::{CheckedAdd, CheckedSub, Encoding, U256};
9use p256::ecdsa::signature::Signer;
10use p256::ecdsa::{Signature, SigningKey};
11use std::io::Write;
12use std::sync::LazyLock;
13use std::time::SystemTime;
14use zeroize::Zeroizing;
15
16const ALGORITHM: &[u8] = b"AWS4-ECDSA-P256-SHA256";
17static BIG_N_MINUS_2: LazyLock<U256> = LazyLock::new(|| {
18    // The N value from section 3.2.1.3 of https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-186.pdf
19    // Used as the N value for the algorithm described in section A.2.2 of https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-5.pdf
20    // *(Basically a prime number blessed by the NSA for use in p256)*
21    const ORDER: U256 =
22        U256::from_be_hex("ffffffff00000000ffffffffffffffffbce6faada7179e84f3b9cac2fc632551");
23    ORDER.checked_sub(&U256::from(2u32)).unwrap()
24});
25
26/// Calculates a Sigv4a signature
27pub fn calculate_signature(signing_key: impl AsRef<[u8]>, string_to_sign: &[u8]) -> String {
28    let signing_key = SigningKey::from_bytes(signing_key.as_ref()).unwrap();
29    let signature: Signature = signing_key.sign(string_to_sign);
30    // This conversion sucks but we have to do it afaict. Because we also use
31    // the HMAC crate, we have to use a compatible (and therefore older) version
32    // of the p256 crate. That older version requires us to convert between
33    // signature types instead of using DER-encoded signatures directly.
34    let signature = signature.to_der();
35    hex::encode(signature.as_ref())
36}
37
38/// Generates a signing key for Sigv4a signing.
39pub fn generate_signing_key(access_key: &str, secret_access_key: &str) -> impl AsRef<[u8]> {
40    // Capacity is the secret access key length plus the length of "AWS4A"
41    let mut input_key = Zeroizing::new(Vec::with_capacity(secret_access_key.len() + 5));
42    write!(input_key, "AWS4A{secret_access_key}").unwrap();
43
44    // Capacity is the access key length plus the counter byte
45    let mut kdf_context = Zeroizing::new(Vec::with_capacity(access_key.len() + 1));
46    let mut counter = Zeroizing::new(1u8);
47    let key = loop {
48        write!(kdf_context, "{access_key}").unwrap();
49        kdf_context.push(*counter);
50
51        let mut fis = ALGORITHM.to_vec();
52        fis.push(0);
53        fis.append(&mut kdf_context);
54        fis.put_i32(256);
55
56        let key = ring::hmac::Key::new(ring::hmac::HMAC_SHA256, &input_key);
57
58        let mut buf = BytesMut::new();
59        buf.put_i32(1);
60        buf.put_slice(&fis);
61        let tag = ring::hmac::sign(&key, &buf);
62        let tag = &tag.as_ref()[0..32];
63
64        let k0 = U256::from_be_bytes(tag.try_into().expect("convert to [u8; 32]"));
65
66        // It would be more secure for this to be a constant time comparison, but because this
67        // is for client usage, that's not as big a deal.
68        if k0 <= *BIG_N_MINUS_2 {
69            let pk = k0
70                .checked_add(&U256::ONE)
71                .expect("k0 is always less than U256::MAX");
72            let d = Zeroizing::new(pk.to_be_bytes());
73            break SigningKey::from_bytes(d.as_ref()).unwrap();
74        }
75
76        *counter = counter
77            .checked_add(1)
78            .expect("counter will never get to 255");
79    };
80
81    key.to_bytes()
82}
83
84/// Parameters to use when signing.
85#[derive(Debug)]
86#[non_exhaustive]
87pub struct SigningParams<'a, S> {
88    /// The identity to use when signing a request
89    pub(crate) identity: &'a Identity,
90
91    /// Region set to sign for.
92    pub(crate) region_set: &'a str,
93    /// Service Name to sign for.
94    ///
95    /// NOTE: Endpoint resolution rules may specify a name that differs from the typical service name.
96    pub(crate) name: &'a str,
97    /// Timestamp to use in the signature (should be `SystemTime::now()` unless testing).
98    pub(crate) time: SystemTime,
99
100    /// Additional signing settings. These differ between HTTP and Event Stream.
101    pub(crate) settings: S,
102}
103
104pub(crate) const ECDSA_256: &str = "AWS4-ECDSA-P256-SHA256";
105
106impl<S> SigningParams<'_, S> {
107    /// Returns the region that will be used to sign SigV4a requests
108    pub fn region_set(&self) -> &str {
109        self.region_set
110    }
111
112    /// Returns the service name that will be used to sign requests
113    pub fn name(&self) -> &str {
114        self.name
115    }
116
117    /// Return the name of the algorithm used to sign requests
118    pub fn algorithm(&self) -> &'static str {
119        ECDSA_256
120    }
121}
122
123impl<'a, S: Default> SigningParams<'a, S> {
124    /// Returns a builder that can create new `SigningParams`.
125    pub fn builder() -> signing_params::Builder<'a, S> {
126        Default::default()
127    }
128}
129
130/// Builder and error for creating [`SigningParams`]
131pub mod signing_params {
132    use super::SigningParams;
133    use aws_smithy_runtime_api::client::identity::Identity;
134    use std::error::Error;
135    use std::fmt;
136    use std::time::SystemTime;
137
138    /// [`SigningParams`] builder error
139    #[derive(Debug)]
140    pub struct BuildError {
141        reason: &'static str,
142    }
143    impl BuildError {
144        fn new(reason: &'static str) -> Self {
145            Self { reason }
146        }
147    }
148
149    impl fmt::Display for BuildError {
150        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
151            write!(f, "{}", self.reason)
152        }
153    }
154
155    impl Error for BuildError {}
156
157    /// Builder that can create new [`SigningParams`]
158    #[derive(Debug, Default)]
159    pub struct Builder<'a, S> {
160        identity: Option<&'a Identity>,
161        region_set: Option<&'a str>,
162        name: Option<&'a str>,
163        time: Option<SystemTime>,
164        settings: Option<S>,
165    }
166
167    impl<'a, S> Builder<'a, S> {
168        builder_methods!(
169            set_identity,
170            identity,
171            &'a Identity,
172            "Sets the identity (required)",
173            set_region_set,
174            region_set,
175            &'a str,
176            "Sets the region set (required)",
177            set_name,
178            name,
179            &'a str,
180            "Sets the name (required)",
181            set_time,
182            time,
183            SystemTime,
184            "Sets the time to be used in the signature (required)",
185            set_settings,
186            settings,
187            S,
188            "Sets additional signing settings (required)"
189        );
190
191        /// Builds an instance of [`SigningParams`]. Will yield a [`BuildError`] if
192        /// a required argument was not given.
193        pub fn build(self) -> Result<SigningParams<'a, S>, BuildError> {
194            Ok(SigningParams {
195                identity: self
196                    .identity
197                    .ok_or_else(|| BuildError::new("identity is required"))?,
198                region_set: self
199                    .region_set
200                    .ok_or_else(|| BuildError::new("region_set is required"))?,
201                name: self
202                    .name
203                    .ok_or_else(|| BuildError::new("name is required"))?,
204                time: self
205                    .time
206                    .ok_or_else(|| BuildError::new("time is required"))?,
207                settings: self
208                    .settings
209                    .ok_or_else(|| BuildError::new("settings are required"))?,
210            })
211        }
212    }
213}
aws_sigv4/sign/v4a.rs

aws_sigv4/sign/
v4a.rs
