sm2: support ASN.1 DER signature format for SM2DSA (#1358)

Author: heliannuuthus

sm2/Cargo.toml

@@ -28,6 +28,7 @@ rfc6979 = { version = "0.5.0-rc.0", optional = true }
 serdect = { version = "0.3", optional = true, default-features = false }
 signature = { version = "3.0.0-rc.1", optional = true, features = ["rand_core"] }
 sm3 = { version = "0.5.0-rc.0", optional = true, default-features = false }
+der = { version = "0.8.0-rc.7", optional = true }
 
 [dev-dependencies]
 hex-literal = "1"
@@ -44,7 +45,7 @@ bits = ["arithmetic", "elliptic-curve/bits"]
 dsa = ["arithmetic", "dep:rfc6979", "dep:signature", "dep:sm3"]
 pke = ["arithmetic", "dep:sm3"]
 pem = ["elliptic-curve/pem", "pkcs8"]
-pkcs8 = ["elliptic-curve/pkcs8"]
+pkcs8 = ["elliptic-curve/pkcs8", "der"]
 serde = ["elliptic-curve/serde", "primeorder?/serde", "serdect"]
 
 [package.metadata.docs.rs]

sm2/src/dsa.rs

@@ -38,27 +38,43 @@ mod signing;
 #[cfg(feature = "arithmetic")]
 mod verifying;
 
+#[cfg(feature = "der")]
+mod der;
+
+#[cfg(feature = "der")]
+pub use der::Signature as DerSignature;
+
 pub use signature;
 
 #[cfg(feature = "arithmetic")]
 pub use self::{signing::SigningKey, verifying::VerifyingKey};
 
-use crate::{FieldBytes, NonZeroScalar, Sm2};
-use core::fmt::{self, Debug};
+use crate::{Array, FieldBytes, FieldBytesSize, NonZeroScalar, Sm2};
+use core::{
+    fmt::{self, Debug},
+    ops::Add,
+};
+
 use signature::{Error, Result, SignatureEncoding};
 
 #[cfg(feature = "alloc")]
 use alloc::vec::Vec;
 
 #[cfg(feature = "pkcs8")]
 use crate::pkcs8::{
-    AlgorithmIdentifierRef, ObjectIdentifier, der::AnyRef, spki::AssociatedAlgorithmIdentifier,
+    AlgorithmIdentifierRef, ObjectIdentifier,
+    der::{self as der_core, AnyRef, asn1::BitString},
+    spki::AssociatedAlgorithmIdentifier,
 };
+
 #[cfg(all(feature = "alloc", feature = "pkcs8"))]
-use crate::pkcs8::{der, spki::SignatureBitStringEncoding};
+use crate::pkcs8::spki::SignatureBitStringEncoding;
 
-/// SM2DSA signature serialized as bytes.
-pub type SignatureBytes = [u8; Signature::BYTE_SIZE];
+/// SM2DSA signature size.
+pub type SignatureSize = <FieldBytesSize as Add>::Output;
+
+/// SM2DSA signature bytes.
+pub type SignatureBytes = Array<u8, SignatureSize>;
 
 /// Primitive scalar type (works without the `arithmetic` feature).
 type ScalarPrimitive = elliptic_curve::ScalarPrimitive<Sm2>;
@@ -101,9 +117,15 @@ impl Signature {
         Self::try_from(r.into().concat(s.into()).as_slice())
     }
 
+    /// Parse a signature from ASN.1 DER.
+    #[cfg(feature = "der")]
+    pub fn from_der(bytes: &[u8]) -> Result<Self> {
+        DerSignature::try_from(bytes).and_then(Self::try_from)
+    }
+
     /// Serialize this signature as bytes.
     pub fn to_bytes(&self) -> SignatureBytes {
-        let mut ret = [0; Self::BYTE_SIZE];
+        let mut ret = SignatureBytes::default();
         let (r_bytes, s_bytes) = ret.split_at_mut(Self::BYTE_SIZE / 2);
         r_bytes.copy_from_slice(&self.r.to_bytes());
         s_bytes.copy_from_slice(&self.s.to_bytes());
@@ -120,6 +142,12 @@ impl Signature {
         self.s.to_bytes()
     }
 
+    /// Serialize this signature as ASN.1 DER.
+    #[cfg(feature = "der")]
+    pub fn to_der(&self) -> DerSignature {
+        DerSignature::from_components(&self.r_bytes(), &self.s_bytes()).expect("DER encoding error")
+    }
+
     /// Convert this signature into a byte vector.
     #[cfg(feature = "alloc")]
     pub fn to_vec(&self) -> Vec<u8> {
@@ -207,8 +235,8 @@ impl TryFrom<&[u8]> for Signature {
 
 #[cfg(all(feature = "alloc", feature = "pkcs8"))]
 impl SignatureBitStringEncoding for Signature {
-    fn to_bitstring(&self) -> der::Result<der::asn1::BitString> {
-        der::asn1::BitString::new(0, self.to_vec())
+    fn to_bitstring(&self) -> der_core::Result<BitString> {
+        BitString::new(0, self.to_vec())
     }
 }