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// 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. //! ECDSA Signatures using the P-256 and P-384 curves. use arithmetic::montgomery::*; use core; use {der, digest, ec, error, pkcs8, private, rand, signature}; use super::verify_jacobian_point_is_on_the_curve; use super::ops::*; use super::public_key::*; use untrusted; /// An ECDSA signing algorithm. pub struct ECDSASigningAlgorithm { curve: &'static ec::Curve, pkcs8_template: &'static pkcs8::Template, id: ECDSASigningAlgorithmID } #[allow(non_camel_case_types)] #[derive(PartialEq, Eq)] enum ECDSASigningAlgorithmID { ECDSA_P256_SHA256_FIXED_SIGNING, ECDSA_P384_SHA384_FIXED_SIGNING, ECDSA_P256_SHA256_ASN1_SIGNING, ECDSA_P384_SHA384_ASN1_SIGNING, } impl PartialEq for ECDSASigningAlgorithm { fn eq(&self, other: &Self) -> bool { self.id == other.id } } impl Eq for ECDSASigningAlgorithm {} /// An ECDSA verification algorithm. pub struct ECDSAVerificationAlgorithm { ops: &'static PublicScalarOps, digest_alg: &'static digest::Algorithm, split_rs: for<'a> fn(ops: &'static ScalarOps, input: &mut untrusted::Reader<'a>) -> Result<(untrusted::Input<'a>, untrusted::Input<'a>), error::Unspecified>, id: ECDSAVerificationAlgorithmID, } #[allow(non_camel_case_types)] enum ECDSAVerificationAlgorithmID { ECDSA_P256_SHA256_ASN1, ECDSA_P256_SHA256_FIXED, ECDSA_P256_SHA384_ASN1, ECDSA_P384_SHA256_ASN1, ECDSA_P384_SHA384_ASN1, ECDSA_P384_SHA384_FIXED, } impl core::fmt::Debug for ECDSAVerificationAlgorithm { fn fmt(&self, f: &mut core::fmt::Formatter) -> Result<(), core::fmt::Error> { use self::ECDSAVerificationAlgorithmID::*; write!(f, "ring::signature::{}", match self.id { ECDSA_P256_SHA256_ASN1 => "ECDSA_P256_SHA256_ASN1", ECDSA_P256_SHA256_FIXED => "ECDSA_P256_SHA256_FIXED", ECDSA_P256_SHA384_ASN1 => "ECDSA_P256_SHA384_ASN1", ECDSA_P384_SHA256_ASN1 => "ECDSA_P384_SHA256_ASN1", ECDSA_P384_SHA384_ASN1 => "ECDSA_P384_SHA384_ASN1", ECDSA_P384_SHA384_FIXED => "ECDSA_P384_SHA384_FIXED", }) } } impl signature::VerificationAlgorithm for ECDSAVerificationAlgorithm { // Verify an ECDSA signature as documented in the NSA Suite B Implementer's // Guide to ECDSA Section 3.4.2: ECDSA Signature Verification. fn verify(&self, public_key: untrusted::Input, msg: untrusted::Input, signature: untrusted::Input) -> Result<(), error::Unspecified> { let public_key_ops = self.ops.public_key_ops; let scalar_ops = self.ops.scalar_ops; // NSA Guide Prerequisites: // // Prior to accepting a verified digital signature as valid the // verifier shall have: // // 1. assurance of the signatory’s claimed identity, // 2. an authentic copy of the domain parameters, (q, FR, a, b, // SEED, G, n, h), // 3. assurance of the validity of the public key, and // 4. assurance that the claimed signatory actually possessed the // private key that was used to generate the digital signature // at the time that the signature was generated. // // Prerequisites #1 and #4 are outside the scope of what this function // can do. Prerequisite #2 is handled implicitly as the domain // parameters are hard-coded into the source. Prerequisite #3 is // handled by `parse_uncompressed_point`. let peer_pub_key = parse_uncompressed_point(public_key_ops, public_key)?; let (r, s) = signature.read_all( error::Unspecified, |input| (self.split_rs)(scalar_ops, input))?; // NSA Guide Step 1: "If r and s are not both integers in the interval // [1, n − 1], output INVALID." let r = scalar_parse_big_endian_variable(public_key_ops.common, AllowZero::No, r)?; let s = scalar_parse_big_endian_variable(public_key_ops.common, AllowZero::No, s)?; // NSA Guide Step 2: "Use the selected hash function to compute H = // Hash(M)." // NSA Guide Step 3: "Convert the bit string H to an integer e as // described in Appendix B.2." let e = digest_scalar(scalar_ops, self.digest_alg, msg); // NSA Guide Step 4: "Compute w = s**−1 mod n, using the routine in // Appendix B.1." let w = scalar_ops.scalar_inv_to_mont(&s); // NSA Guide Step 5: "Compute u1 = (e * w) mod n, and compute // u2 = (r * w) mod n." let u1 = scalar_ops.scalar_product(&e, &w); let u2 = scalar_ops.scalar_product(&r, &w); // NSA Guide Step 6: "Compute the elliptic curve point // R = (xR, yR) = u1*G + u2*Q, using EC scalar multiplication and EC // addition. If R is equal to the point at infinity, output INVALID." let product = twin_mul(self.ops.private_key_ops, &u1, &u2, &peer_pub_key); // Verify that the point we computed is on the curve; see // `verify_affine_point_is_on_the_curve_scaled` for details on why. It // would be more secure to do the check on the affine coordinates if we // were going to convert to affine form (again, see // `verify_affine_point_is_on_the_curve_scaled` for details on why). // But, we're going to avoid converting to affine for performance // reasons, so we do the verification using the Jacobian coordinates. let z2 = verify_jacobian_point_is_on_the_curve(public_key_ops.common, &product)?; // NSA Guide Step 7: "Compute v = xR mod n." // NSA Guide Step 8: "Compare v and r0. If v = r0, output VALID; // otherwise, output INVALID." // // Instead, we use Greg Maxwell's trick to avoid the inversion mod `q` // that would be necessary to compute the affine X coordinate. let x = public_key_ops.common.point_x(&product); fn sig_r_equals_x(ops: &PublicScalarOps, r: &Elem<Unencoded>, x: &Elem<R>, z2: &Elem<R>) -> bool { let cops = ops.public_key_ops.common; let r_jacobian = cops.elem_product(z2, r); let x = cops.elem_unencoded(x); ops.elem_equals(&r_jacobian, &x) } let r = self.ops.scalar_as_elem(&r); if sig_r_equals_x(self.ops, &r, &x, &z2) { return Ok(()); } if self.ops.elem_less_than(&r, &self.ops.q_minus_n) { let r_plus_n = self.ops.elem_sum(&r, &public_key_ops.common.n); if sig_r_equals_x(self.ops, &r_plus_n, &x, &z2) { return Ok(()); } } Err(error::Unspecified) } } impl private::Private for ECDSAVerificationAlgorithm {} /// An ECDSA key pair, used for signing. #[doc(hidden)] pub struct ECDSAKeyPair { #[allow(dead_code)] // XXX: Temporary, since signing isn't implemented yet. key_pair: ec::KeyPair, #[allow(dead_code)] // XXX: Temporary, since signing isn't implemented yet. alg: &'static ECDSASigningAlgorithm, } impl<'a> ECDSAKeyPair { /// Generates a new key pair and returns the key pair serialized as a /// PKCS#8 document. /// /// The PKCS#8 document will be a v1 `OneAsymmetricKey` with the public key /// included in the `ECPrivateKey` structure, as described in /// [RFC 5958 Section 2] and [RFC 5915]. The `ECPrivateKey` structure will /// not have a `parameters` field so the generated key is compatible with /// PKCS#11. /// /// [RFC 5915]: https://tools.ietf.org/html/rfc5915 /// [RFC 5958 Section 2]: https://tools.ietf.org/html/rfc5958#section-2 pub fn generate_pkcs8(alg: &'static ECDSASigningAlgorithm, rng: &rand::SecureRandom) -> Result<pkcs8::PKCS8Document, error::Unspecified> { let private_key = ec::PrivateKey::generate(alg.curve, rng)?; let mut public_key_bytes = [0; ec::PUBLIC_KEY_MAX_LEN]; let public_key_bytes = &mut public_key_bytes[..alg.curve.public_key_len]; (alg.curve.public_from_private)(public_key_bytes, &private_key)?; Ok(pkcs8::wrap_key(&alg.pkcs8_template, private_key.bytes(alg.curve), public_key_bytes)) } /// Constructs an ECDSA key pair by parsing an unencrypted PKCS#8 v1 /// id-ecPublicKey `ECPrivateKey` key. /// /// The input must be in PKCS#8 v1 format. It must contain the public key in /// the `ECPrivateKey` structure; `from_pkcs8()` will verify that the public /// key and the private key are consistent with each other. The algorithm /// identifier must identify the curve by name; it must not use an /// "explicit" encoding of the curve. The `parameters` field of the /// `ECPrivateKey`, if present, must be the same named curve that is in the /// algorithm identifier in the PKCS#8 header. pub fn from_pkcs8(alg: &'static ECDSASigningAlgorithm, input: untrusted::Input) -> Result<ECDSAKeyPair, error::Unspecified> { let key_pair = ec::suite_b::key_pair_from_pkcs8(alg.curve, alg.pkcs8_template, input)?; Ok(ECDSAKeyPair { key_pair, alg }) } /// Constructs an ECDSA key pair directly from the big-endian-encoded /// private key and public key bytes. /// /// This is intended for use by code that deserializes key pairs. It is /// recommended to use `ECDSAKeyPair::from_pkcs8()` (with a PKCS#8-encoded /// key) instead. pub fn from_private_key_and_public_key(alg: &'static ECDSASigningAlgorithm, private_key: untrusted::Input, public_key: untrusted::Input) -> Result<ECDSAKeyPair, error::Unspecified> { let key_pair = ec::suite_b::key_pair_from_bytes( alg.curve, private_key, public_key)?; Ok(ECDSAKeyPair { key_pair, alg }) } } fn split_rs_fixed<'a>( ops: &'static ScalarOps, input: &mut untrusted::Reader<'a>) -> Result<(untrusted::Input<'a>, untrusted::Input<'a>), error::Unspecified> { let scalar_len = ops.scalar_bytes_len(); let r = input.skip_and_get_input(scalar_len)?; let s = input.skip_and_get_input(scalar_len)?; Ok((r, s)) } fn split_rs_asn1<'a>( _ops: &'static ScalarOps, input: &mut untrusted::Reader<'a>) -> Result<(untrusted::Input<'a>, untrusted::Input<'a>), error::Unspecified> { der::nested(input, der::Tag::Sequence, error::Unspecified, |input| { let r = der::positive_integer(input)?; let s = der::positive_integer(input)?; Ok((r, s)) }) } /// 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. fn digest_scalar(ops: &ScalarOps, digest_alg: &'static digest::Algorithm, msg: untrusted::Input) -> Scalar { let digest = digest::digest(digest_alg, msg.as_slice_less_safe()); digest_scalar_(ops, digest.as_ref()) } // This is a separate function solely so that we can test specific digest // values like all-zero values and values larger than `n`. fn digest_scalar_(ops: &ScalarOps, digest: &[u8]) -> Scalar { let cops = ops.common; let num_limbs = cops.num_limbs; let digest = if digest.len() > num_limbs * LIMB_BYTES { &digest[..(num_limbs * LIMB_BYTES)] } else { digest }; scalar_parse_big_endian_partially_reduced_variable_consttime( cops, AllowZero::Yes, untrusted::Input::from(digest)).unwrap() } fn twin_mul(ops: &PrivateKeyOps, g_scalar: &Scalar, p_scalar: &Scalar, p_xy: &(Elem<R>, Elem<R>)) -> Point { // XXX: Inefficient. TODO: implement interleaved wNAF multiplication. let scaled_g = ops.point_mul_base(g_scalar); let scaled_p = ops.point_mul(p_scalar, p_xy); ops.common.point_sum(&scaled_g, &scaled_p) } /// Signing of fixed-length (PKCS#11 style) ECDSA signatures using the /// P-256 curve and SHA-256. /// /// See "`ECDSA_*_FIXED` Details" in `ring::signature`'s module-level /// documentation for more details. #[doc(hidden)] pub static ECDSA_P256_SHA256_FIXED_SIGNING: ECDSASigningAlgorithm = ECDSASigningAlgorithm { curve: &ec::suite_b::curve::P256, pkcs8_template: &EC_PUBLIC_KEY_P256_PKCS8_V1_TEMPLATE, id: ECDSASigningAlgorithmID::ECDSA_P256_SHA256_FIXED_SIGNING, }; /// Verification of fixed-length (PKCS#11 style) ECDSA signatures using the /// P-256 curve and SHA-256. /// /// See "`ECDSA_*_FIXED` Details" in `ring::signature`'s module-level /// documentation for more details. pub static ECDSA_P256_SHA256_FIXED: ECDSAVerificationAlgorithm = ECDSAVerificationAlgorithm { ops: &p256::PUBLIC_SCALAR_OPS, digest_alg: &digest::SHA256, split_rs: split_rs_fixed, id: ECDSAVerificationAlgorithmID::ECDSA_P256_SHA256_FIXED, }; /// Signing of fixed-length (PKCS#11 style) ECDSA signatures using the /// P-384 curve and SHA-384. /// /// See "`ECDSA_*_FIXED` Details" in `ring::signature`'s module-level /// documentation for more details. #[doc(hidden)] pub static ECDSA_P384_SHA384_FIXED_SIGNING: ECDSASigningAlgorithm = ECDSASigningAlgorithm { curve: &ec::suite_b::curve::P384, pkcs8_template: &EC_PUBLIC_KEY_P384_PKCS8_V1_TEMPLATE, id: ECDSASigningAlgorithmID::ECDSA_P384_SHA384_FIXED_SIGNING, }; /// Verification of fixed-length (PKCS#11 style) ECDSA signatures using the /// P-384 curve and SHA-384. /// /// See "`ECDSA_*_FIXED` Details" in `ring::signature`'s module-level /// documentation for more details. pub static ECDSA_P384_SHA384_FIXED: ECDSAVerificationAlgorithm = ECDSAVerificationAlgorithm { ops: &p384::PUBLIC_SCALAR_OPS, digest_alg: &digest::SHA384, split_rs: split_rs_fixed, id: ECDSAVerificationAlgorithmID::ECDSA_P384_SHA384_FIXED, }; /// Signing of ASN.1 DER-encoded ECDSA signatures using the P-256 curve and /// SHA-256. /// /// See "`ECDSA_*_ASN1` Details" in `ring::signature`'s module-level /// documentation for more details. #[doc(hidden)] pub static ECDSA_P256_SHA256_ASN1_SIGNING: ECDSASigningAlgorithm = ECDSASigningAlgorithm { curve: &ec::suite_b::curve::P256, pkcs8_template: &EC_PUBLIC_KEY_P256_PKCS8_V1_TEMPLATE, id: ECDSASigningAlgorithmID::ECDSA_P256_SHA256_ASN1_SIGNING, }; /// Verification of ASN.1 DER-encoded ECDSA signatures using the P-256 curve /// and SHA-256. /// /// See "`ECDSA_*_ASN1` Details" in `ring::signature`'s module-level /// documentation for more details. pub static ECDSA_P256_SHA256_ASN1: ECDSAVerificationAlgorithm = ECDSAVerificationAlgorithm { ops: &p256::PUBLIC_SCALAR_OPS, digest_alg: &digest::SHA256, split_rs: split_rs_asn1, id: ECDSAVerificationAlgorithmID::ECDSA_P256_SHA256_ASN1, }; /// *Not recommended*. Verification of ASN.1 DER-encoded ECDSA signatures using /// the P-256 curve and SHA-384. /// /// In most situations, P-256 should be used only with SHA-256 and P-384 /// should be used only with SHA-384. However, in some cases, particularly TLS /// on the web, it is necessary to support P-256 with SHA-384 for compatibility /// with widely-deployed implementations that do not follow these guidelines. /// /// See "`ECDSA_*_ASN1` Details" in `ring::signature`'s module-level /// documentation for more details. pub static ECDSA_P256_SHA384_ASN1: ECDSAVerificationAlgorithm = ECDSAVerificationAlgorithm { ops: &p256::PUBLIC_SCALAR_OPS, digest_alg: &digest::SHA384, split_rs: split_rs_asn1, id: ECDSAVerificationAlgorithmID::ECDSA_P256_SHA384_ASN1, }; /// *Not recommended*. Verification of ASN.1 DER-encoded ECDSA signatures using /// the P-384 curve and SHA-256. /// /// In most situations, P-256 should be used only with SHA-256 and P-384 /// should be used only with SHA-384. However, in some cases, particularly TLS /// on the web, it is necessary to support P-256 with SHA-384 for compatibility /// with widely-deployed implementations that do not follow these guidelines. /// /// See "`ECDSA_*_ASN1` Details" in `ring::signature`'s module-level /// documentation for more details. pub static ECDSA_P384_SHA256_ASN1: ECDSAVerificationAlgorithm = ECDSAVerificationAlgorithm { ops: &p384::PUBLIC_SCALAR_OPS, digest_alg: &digest::SHA256, split_rs: split_rs_asn1, id: ECDSAVerificationAlgorithmID::ECDSA_P384_SHA256_ASN1, }; /// Signing of ASN.1 DER-encoded ECDSA signatures using the P-384 curve and /// SHA-384. /// /// See "`ECDSA_*_ASN1` Details" in `ring::signature`'s module-level /// documentation for more details. #[doc(hidden)] pub static ECDSA_P384_SHA384_ASN1_SIGNING: ECDSASigningAlgorithm = ECDSASigningAlgorithm { curve: &ec::suite_b::curve::P384, pkcs8_template: &EC_PUBLIC_KEY_P384_PKCS8_V1_TEMPLATE, id: ECDSASigningAlgorithmID::ECDSA_P384_SHA384_ASN1_SIGNING, }; /// Verification of ASN.1 DER-encoded ECDSA signatures using the P-384 curve /// and SHA-384. /// /// See "`ECDSA_*_ASN1` Details" in `ring::signature`'s module-level /// documentation for more details. pub static ECDSA_P384_SHA384_ASN1: ECDSAVerificationAlgorithm = ECDSAVerificationAlgorithm { ops: &p384::PUBLIC_SCALAR_OPS, digest_alg: &digest::SHA384, split_rs: split_rs_asn1, id: ECDSAVerificationAlgorithmID::ECDSA_P384_SHA384_ASN1, }; static EC_PUBLIC_KEY_P256_PKCS8_V1_TEMPLATE: pkcs8::Template = pkcs8::Template { bytes: include_bytes ! ("ecPublicKey_p256_pkcs8_v1_template.der"), alg_id_range: core::ops::Range { start: 8, end: 27 }, curve_id_index: 9, private_key_index: 0x24, }; static EC_PUBLIC_KEY_P384_PKCS8_V1_TEMPLATE: pkcs8::Template = pkcs8::Template { bytes: include_bytes!("ecPublicKey_p384_pkcs8_v1_template.der"), alg_id_range: core::ops::Range { start: 8, end: 24 }, curve_id_index: 9, private_key_index: 0x23, }; #[cfg(test)] mod tests { use {digest, test}; use super::digest_scalar_; use super::super::ops::*; use untrusted; #[test] fn ecdsa_digest_scalar_test() { test::from_file("src/ec/suite_b/ecdsa_digest_scalar_tests.txt", |section, test_case| { assert_eq!(section, ""); let curve_name = test_case.consume_string("Curve"); let digest_name = test_case.consume_string("Digest"); let input = test_case.consume_bytes("Input"); let output = test_case.consume_bytes("Output"); let (ops, digest_alg) = match (curve_name.as_str(), digest_name.as_str()) { ("P-256", "SHA256") => (&p256::PUBLIC_SCALAR_OPS, &digest::SHA256), ("P-256", "SHA384") => (&p256::PUBLIC_SCALAR_OPS, &digest::SHA384), ("P-384", "SHA256") => (&p384::PUBLIC_SCALAR_OPS, &digest::SHA256), ("P-384", "SHA384") => (&p384::PUBLIC_SCALAR_OPS, &digest::SHA384), _ => { panic!("Unsupported curve+digest: {}+{}", curve_name, digest_name); } }; let num_limbs = ops.public_key_ops.common.num_limbs; assert_eq!(input.len(), digest_alg.output_len); assert_eq!(output.len(), ops.public_key_ops.common.num_limbs * LIMB_BYTES); let expected = scalar_parse_big_endian_variable( ops.public_key_ops.common, AllowZero::Yes, untrusted::Input::from(&output)).unwrap(); let actual = digest_scalar_(ops.scalar_ops, &input); assert_eq!(actual.limbs[..num_limbs], expected.limbs[..num_limbs]); Ok(()) }); } }