ring/ec/suite_b/
public_key.rs

1// Copyright 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 AUTHOR DISCLAIMS ALL WARRANTIES
8// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR 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//! Functionality shared by operations on public keys (ECDSA verification and
16//! ECDH agreement).
17
18use super::{ops::*, verify_affine_point_is_on_the_curve};
19use crate::{arithmetic::montgomery::*, error};
20
21/// Parses a public key encoded in uncompressed form. The key is validated
22/// using the ECC Partial Public-Key Validation Routine from
23/// [NIST SP 800-56A, revision 2] Section 5.6.2.3.3, the NSA's
24/// "Suite B Implementer's Guide to NIST SP 800-56A," Appendix B.3, and the
25/// NSA's "Suite B Implementer's Guide to FIPS 186-3 (ECDSA)," Appendix A.3.
26///
27/// [NIST SP 800-56A, revision 2]:
28///     http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-56Ar2.pdf
29pub(super) fn parse_uncompressed_point(
30    ops: &PublicKeyOps,
31    q: &Modulus<Q>,
32    input: untrusted::Input,
33) -> Result<(Elem<R>, Elem<R>), error::Unspecified> {
34    // NIST SP 800-56A Step 1: "Verify that Q is not the point at infinity.
35    // This can be done by inspection if the point is entered in the standard
36    // affine representation." (We do it by inspection since we only accept
37    // the affine representation.)
38    let (x, y) = input.read_all(error::Unspecified, |input| {
39        // The encoding must be 4, which is the encoding for "uncompressed".
40        let encoding = input.read_byte()?;
41        if encoding != 4 {
42            return Err(error::Unspecified);
43        }
44
45        // NIST SP 800-56A Step 2: "Verify that xQ and yQ are integers in the
46        // interval [0, p-1] in the case that q is an odd prime p[.]"
47        let x = ops.elem_parse(q, input)?;
48        let y = ops.elem_parse(q, input)?;
49        Ok((x, y))
50    })?;
51
52    // NIST SP 800-56A Step 3: "If q is an odd prime p, verify that
53    // yQ**2 = xQ**3 + axQ + b in GF(p), where the arithmetic is performed
54    // modulo p."
55    verify_affine_point_is_on_the_curve(q, (&x, &y))?;
56
57    // NIST SP 800-56A Note: "Since its order is not verified, there is no
58    // check that the public key is in the correct EC subgroup."
59    //
60    // NSA Suite B Implementer's Guide Note: "ECC Full Public-Key Validation
61    // includes an additional check to ensure that the point has the correct
62    // order. This check is not necessary for curves having prime order (and
63    // cofactor h = 1), such as P-256 and P-384."
64
65    Ok((x, y))
66}
67
68#[cfg(test)]
69mod tests {
70    use super::*;
71    use crate::{cpu, test};
72
73    #[test]
74    fn parse_uncompressed_point_test() {
75        let cpu = cpu::features();
76        test::run(
77            test_file!("suite_b_public_key_tests.txt"),
78            |section, test_case| {
79                assert_eq!(section, "");
80
81                let curve_name = test_case.consume_string("Curve");
82
83                let public_key = test_case.consume_bytes("Q");
84                let public_key = untrusted::Input::from(&public_key);
85                let is_valid = test_case.consume_string("Result") == "P";
86
87                let curve_ops = public_key_ops_from_curve_name(&curve_name);
88                let q = &curve_ops.common.elem_modulus(cpu);
89
90                let result = parse_uncompressed_point(curve_ops, q, public_key);
91                assert_eq!(is_valid, result.is_ok());
92
93                // TODO: Verify that we when we re-serialize the parsed (x, y), the
94                // output is equal to the input.
95
96                Ok(())
97            },
98        );
99    }
100
101    fn public_key_ops_from_curve_name(curve_name: &str) -> &'static PublicKeyOps {
102        if curve_name == "P-256" {
103            &p256::PUBLIC_KEY_OPS
104        } else if curve_name == "P-384" {
105            &p384::PUBLIC_KEY_OPS
106        } else {
107            panic!("Unsupported curve: {}", curve_name);
108        }
109    }
110}