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 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//! 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}
111