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| </pre><pre class="rust"><code><span class="comment">// Copyright 2015-2016 Brian Smith. |
| // |
| // Permission to use, copy, modify, and/or distribute this software for any |
| // purpose with or without fee is hereby granted, provided that the above |
| // copyright notice and this permission notice appear in all copies. |
| // |
| // THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES |
| // WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF |
| // MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY |
| // SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES |
| // WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION |
| // OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN |
| // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. |
| |
| </span><span class="doccomment">//! ECDSA Signatures using the P-256 and P-384 curves. |
| |
| </span><span class="kw">use crate</span>::{ |
| digest, |
| ec::suite_b::ops::<span class="kw-2">*</span>, |
| limb::{<span class="self">self</span>, LIMB_BYTES}, |
| }; |
| |
| <span class="doccomment">/// Calculate the digest of `msg` using the digest algorithm `digest_alg`. Then |
| /// convert the digest to a scalar in the range [0, n) as described in |
| /// NIST's FIPS 186-4 Section 4.2. Note that this is one of the few cases where |
| /// a `Scalar` is allowed to have the value zero. |
| /// |
| /// NIST's FIPS 186-4 4.2 says "When the length of the output of the hash |
| /// function is greater than N (i.e., the bit length of q), then the leftmost N |
| /// bits of the hash function output block shall be used in any calculation |
| /// using the hash function output during the generation or verification of a |
| /// digital signature." |
| /// |
| /// "Leftmost N bits" means "N most significant bits" because we interpret the |
| /// digest as a bit-endian encoded integer. |
| /// |
| /// The NSA guide instead vaguely suggests that we should convert the digest |
| /// value to an integer and then reduce it mod `n`. However, real-world |
| /// implementations (e.g. `digest_to_bn` in OpenSSL and `hashToInt` in Go) do |
| /// what FIPS 186-4 says to do, not what the NSA guide suggests. |
| /// |
| /// Why shifting the value right by at most one bit is sufficient: P-256's `n` |
| /// has its 256th bit set; i.e. 2**255 < n < 2**256. Once we've truncated the |
| /// digest to 256 bits and converted it to an integer, it will have a value |
| /// less than 2**256. If the value is larger than `n` then shifting it one bit |
| /// right will give a value less than 2**255, which is less than `n`. The |
| /// analogous argument applies for P-384. However, it does *not* apply in |
| /// general; for example, it doesn't apply to P-521. |
| </span><span class="kw">pub fn </span>digest_scalar(ops: <span class="kw-2">&</span>ScalarOps, msg: digest::Digest) -> Scalar { |
| digest_scalar_(ops, msg.as_ref()) |
| } |
| |
| <span class="attribute">#[cfg(test)] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>digest_bytes_scalar(ops: <span class="kw-2">&</span>ScalarOps, digest: <span class="kw-2">&</span>[u8]) -> Scalar { |
| digest_scalar_(ops, digest) |
| } |
| |
| <span class="comment">// This is a separate function solely so that we can test specific digest |
| // values like all-zero values and values larger than `n`. |
| </span><span class="kw">fn </span>digest_scalar_(ops: <span class="kw-2">&</span>ScalarOps, digest: <span class="kw-2">&</span>[u8]) -> Scalar { |
| <span class="kw">let </span>cops = ops.common; |
| <span class="kw">let </span>num_limbs = cops.num_limbs; |
| <span class="kw">let </span>digest = <span class="kw">if </span>digest.len() > num_limbs * LIMB_BYTES { |
| <span class="kw-2">&</span>digest[..(num_limbs * LIMB_BYTES)] |
| } <span class="kw">else </span>{ |
| digest |
| }; |
| |
| scalar_parse_big_endian_partially_reduced_variable_consttime( |
| cops, |
| limb::AllowZero::Yes, |
| untrusted::Input::from(digest), |
| ) |
| .unwrap() |
| } |
| |
| <span class="attribute">#[cfg(test)] |
| </span><span class="kw">mod </span>tests { |
| <span class="kw">use </span><span class="kw">super</span>::digest_bytes_scalar; |
| <span class="kw">use crate</span>::{ |
| digest, |
| ec::suite_b::ops::<span class="kw-2">*</span>, |
| limb::{<span class="self">self</span>, LIMB_BYTES}, |
| test, |
| }; |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test() { |
| test::run( |
| <span class="macro">test_file!</span>(<span class="string">"ecdsa_digest_scalar_tests.txt"</span>), |
| |section, test_case| { |
| <span class="macro">assert_eq!</span>(section, <span class="string">""</span>); |
| |
| <span class="kw">let </span>curve_name = test_case.consume_string(<span class="string">"Curve"</span>); |
| <span class="kw">let </span>digest_name = test_case.consume_string(<span class="string">"Digest"</span>); |
| <span class="kw">let </span>input = test_case.consume_bytes(<span class="string">"Input"</span>); |
| <span class="kw">let </span>output = test_case.consume_bytes(<span class="string">"Output"</span>); |
| |
| <span class="kw">let </span>(ops, digest_alg) = <span class="kw">match </span>(curve_name.as_str(), digest_name.as_str()) { |
| (<span class="string">"P-256"</span>, <span class="string">"SHA256"</span>) => (<span class="kw-2">&</span>p256::PUBLIC_SCALAR_OPS, <span class="kw-2">&</span>digest::SHA256), |
| (<span class="string">"P-256"</span>, <span class="string">"SHA384"</span>) => (<span class="kw-2">&</span>p256::PUBLIC_SCALAR_OPS, <span class="kw-2">&</span>digest::SHA384), |
| (<span class="string">"P-384"</span>, <span class="string">"SHA256"</span>) => (<span class="kw-2">&</span>p384::PUBLIC_SCALAR_OPS, <span class="kw-2">&</span>digest::SHA256), |
| (<span class="string">"P-384"</span>, <span class="string">"SHA384"</span>) => (<span class="kw-2">&</span>p384::PUBLIC_SCALAR_OPS, <span class="kw-2">&</span>digest::SHA384), |
| <span class="kw">_ </span>=> { |
| <span class="macro">panic!</span>(<span class="string">"Unsupported curve+digest: {}+{}"</span>, curve_name, digest_name); |
| } |
| }; |
| |
| <span class="kw">let </span>num_limbs = ops.public_key_ops.common.num_limbs; |
| <span class="macro">assert_eq!</span>(input.len(), digest_alg.output_len); |
| <span class="macro">assert_eq!</span>( |
| output.len(), |
| ops.public_key_ops.common.num_limbs * LIMB_BYTES |
| ); |
| |
| <span class="kw">let </span>expected = scalar_parse_big_endian_variable( |
| ops.public_key_ops.common, |
| limb::AllowZero::Yes, |
| untrusted::Input::from(<span class="kw-2">&</span>output), |
| ) |
| .unwrap(); |
| |
| <span class="kw">let </span>actual = digest_bytes_scalar(ops.scalar_ops, <span class="kw-2">&</span>input); |
| |
| <span class="macro">assert_eq!</span>(actual.limbs[..num_limbs], expected.limbs[..num_limbs]); |
| |
| <span class="prelude-val">Ok</span>(()) |
| }, |
| ); |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../../../" data-current-crate="ring" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
