Aded an example for recoverable signatures and recovering the pubkey

Author: elichai

.travis.yml

@@ -37,6 +37,7 @@ script:
   - cargo build --verbose --release
   - cargo test --verbose --release
   - cargo run --example sign_verify
+  - cargo run --example sign_verify_recovery --features=recovery
   - cargo run --example generate_keys --features=rand
   - if [ ${TRAVIS_RUST_VERSION} == "stable" ]; then cargo doc --verbose --features="rand,serde,recovery,endomorphism"; fi
   - if [ ${TRAVIS_RUST_VERSION} == "nightly" ]; then cargo test --verbose --benches --features=unstable; fi

Cargo.toml

@@ -51,6 +51,10 @@ version = "1.0"
 optional = true
 default-features = false
 
+[[example]]
+name = "sign_verify_recovery"
+required-features = ["recovery"]
+
 [[example]]
 name = "sign_verify"
 

examples/sign_verify_recovery.rs

@@ -0,0 +1,47 @@
+
+extern crate bitcoin_hashes;
+extern crate secp256k1;
+
+use bitcoin_hashes::{sha256, Hash};
+use secp256k1::recovery::{RecoverableSignature, RecoveryId};
+use secp256k1::{Error, Message, PublicKey, Secp256k1, SecretKey, Signing, Verification};
+
+fn recover<C: Verification>(secp: &Secp256k1<C>,msg: &[u8],sig: [u8; 64],recovery_id: u8) -> Result<PublicKey, Error> {
+    let msg = sha256::Hash::hash(msg);
+    let msg = Message::from_slice(&msg)?;
+    let id = RecoveryId::from_i32(recovery_id as i32)?;
+    let sig = RecoverableSignature::from_compact(&sig, id)?;
+
+    secp.recover(&msg, &sig)
+}
+
+fn sign_recovery<C: Signing>(secp: &Secp256k1<C>, msg: &[u8], seckey: [u8; 32]) -> Result<RecoverableSignature, Error> {
+    let msg = sha256::Hash::hash(msg);
+    let msg = Message::from_slice(&msg)?;
+    let seckey = SecretKey::from_slice(&seckey)?;
+    Ok(secp.sign_recoverable(&msg, &seckey))
+}
+
+fn main() {
+    let secp = Secp256k1::new();
+
+    let seckey = [
+        59, 148, 11, 85, 134, 130, 61, 253, 2, 174, 59, 70, 27, 180, 51, 107,
+        94, 203, 174, 253, 102, 39, 170, 146, 46, 252, 4, 143, 236, 12, 136, 28,
+    ];
+    let pubkey = PublicKey::from_slice(&[
+        2,
+        29, 21, 35, 7, 198, 183, 43, 14, 208, 65, 139, 14, 112, 205, 128, 231,
+        245, 41, 91, 141, 134, 245, 114, 45, 63, 82, 19, 251, 210, 57, 79, 54,
+    ]).unwrap();
+    let msg = b"This is some message";
+
+    let signature = sign_recovery(&secp, msg, seckey).unwrap();
+
+    let (recovery_id, serialize_sig) = signature.serialize_compact();
+
+    assert_eq!(
+        recover(&secp, msg, serialize_sig, recovery_id.to_i32() as u8),
+        Ok(pubkey)
+    );
+}