Convert signature to ecdsa::Signature

Signed-off-by: Arthur Gautier <arthur.gautier@arista.com>

Author: baloo

tss-esapi/src/structures/signatures.rs

@@ -9,6 +9,15 @@ use crate::{
 use log::error;
 use std::convert::{TryFrom, TryInto};
 
+#[cfg(feature = "abstraction")]
+use {
+    ecdsa::SignatureSize,
+    elliptic_curve::{
+        generic_array::{typenum::Unsigned, ArrayLength},
+        FieldBytes, FieldBytesSize, PrimeCurve,
+    },
+};
+
 /// Type holding RSA signature information.
 ///
 /// For more information about the contents of `signature` see Annex B
@@ -143,3 +152,31 @@ impl TryFrom<TPMS_SIGNATURE_ECC> for EccSignature {
         })
     }
 }
+
+#[cfg(feature = "abstraction")]
+impl<C> TryFrom<EccSignature> for ecdsa::Signature<C>
+where
+    C: PrimeCurve,
+    SignatureSize<C>: ArrayLength<u8>,
+{
+    type Error = Error;
+
+    fn try_from(signature: EccSignature) -> Result<Self> {
+        let r = signature.signature_r().as_slice();
+        let s = signature.signature_s().as_slice();
+
+        if r.len() != FieldBytesSize::<C>::USIZE {
+            return Err(Error::local_error(WrapperErrorKind::InvalidParam));
+        }
+        if s.len() != FieldBytesSize::<C>::USIZE {
+            return Err(Error::local_error(WrapperErrorKind::InvalidParam));
+        }
+
+        let signature = ecdsa::Signature::from_scalars(
+            FieldBytes::<C>::from_slice(r).clone(),
+            FieldBytes::<C>::from_slice(s).clone(),
+        )
+        .map_err(|_| Error::local_error(WrapperErrorKind::InvalidParam))?;
+        Ok(signature)
+    }
+}