Merge rust-bitcoin#3397: Implement Arbitrary for signature types

74a992a Implement Arbitrary for signature types (Shing Him Ng)

Pull request description:

  Implementing `Arbitrary` for some signature types in preparation for rust-bitcoin#3366

ACKs for top commit:
  tcharding:
    ACK 74a992a
  apoelstra:
    ACK 74a992a successfully ran local tests

Tree-SHA512: 8bfab4d70b6c8d51374177764323fe4b2bac5c0ac25ef39162fb95040948f27465f488df2094488aab28bdb9656521269b65f8ad7952ed2c5f91589bce084560

bitcoin/src/crypto/ecdsa.rs

@@ -7,6 +7,8 @@
 use core::str::FromStr;
 use core::{fmt, iter};
 
+#[cfg(feature = "arbitrary")]
+use arbitrary::{Arbitrary, Unstructured};
 use hex::FromHex;
 use internals::{impl_to_hex_from_lower_hex, write_err};
 use io::Write;
@@ -293,6 +295,41 @@ impl From<DecodeError> for ParseSignatureError {
     fn from(e: DecodeError) -> Self { Self::Decode(e) }
 }
 
+#[cfg(feature = "arbitrary")]
+impl<'a> Arbitrary<'a> for Signature {
+    fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {
+        // The valid range of r and s should be between 0 and n-1 where
+        // n = 0xFFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFE BAAEDCE6 AF48A03B BFD25E8C D0364141
+        let high_min = 0x0u128;
+        let high_max = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEu128;
+        let low_min = 0x0u128;
+        let low_max = 0xBAAEDCE6AF48A03BBFD25E8CD0364140u128;
+
+        // Equally weight the chances of getting a minimum value for a signature, maximum value for
+        // a signature, and an arbitrary valid signature
+        let choice = u.int_in_range(0..=2)?;
+        let (high, low) = match choice {
+            0 => (high_min, low_min),
+            1 => (high_max, low_max),
+            _ => (u.int_in_range(high_min..=high_max)?, u.int_in_range(low_min..=low_max)?),
+        };
+
+        // We can use the same bytes for r and s since they're just arbitrary values
+        let mut bytes: [u8; 32] = [0; 32];
+        bytes[..16].copy_from_slice(&high.to_be_bytes());
+        bytes[16..].copy_from_slice(&low.to_be_bytes());
+
+        let mut signature_bytes: [u8; 64] = [0; 64];
+        signature_bytes[..32].copy_from_slice(&bytes);
+        signature_bytes[32..].copy_from_slice(&bytes);
+
+        Ok(Signature{
+            signature: secp256k1::ecdsa::Signature::from_compact(&signature_bytes).unwrap(),
+            sighash_type: EcdsaSighashType::arbitrary(u)?,
+        })
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

bitcoin/src/crypto/sighash.rs

@@ -13,6 +13,8 @@
 
 use core::{fmt, str};
 
+#[cfg(feature = "arbitrary")]
+use arbitrary::{Arbitrary, Unstructured};
 use hashes::{hash_newtype, sha256, sha256d, sha256t, sha256t_tag};
 use internals::write_err;
 use io::Write;
@@ -1467,6 +1469,37 @@ impl<E: std::error::Error + 'static> std::error::Error for SigningDataError<E> {
     }
 }
 
+#[cfg(feature = "arbitrary")]
+impl<'a> Arbitrary<'a> for EcdsaSighashType {
+    fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {
+        let choice = u.int_in_range(0..=5)?;
+        match choice {
+            0 => Ok(EcdsaSighashType::All),
+            1 => Ok(EcdsaSighashType::None),
+            2 => Ok(EcdsaSighashType::Single),
+            3 => Ok(EcdsaSighashType::AllPlusAnyoneCanPay),
+            4 => Ok(EcdsaSighashType::NonePlusAnyoneCanPay),
+            _ => Ok(EcdsaSighashType::SinglePlusAnyoneCanPay)
+        }
+    }
+}
+
+#[cfg(feature = "arbitrary")]
+impl<'a> Arbitrary<'a> for TapSighashType {
+    fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {
+        let choice = u.int_in_range(0..=6)?;
+        match choice {
+            0 => Ok(TapSighashType::Default),
+            1 => Ok(TapSighashType::All),
+            2 => Ok(TapSighashType::None),
+            3 => Ok(TapSighashType::Single),
+            4 => Ok(TapSighashType::AllPlusAnyoneCanPay),
+            5 => Ok(TapSighashType::NonePlusAnyoneCanPay),
+            _ => Ok(TapSighashType::SinglePlusAnyoneCanPay)
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use hashes::HashEngine;

bitcoin/src/crypto/taproot.rs

@@ -6,6 +6,8 @@
 
 use core::fmt;
 
+#[cfg(feature = "arbitrary")]
+use arbitrary::{Arbitrary, Unstructured};
 use internals::write_err;
 use io::Write;
 
@@ -133,3 +135,15 @@ impl From<secp256k1::Error> for SigFromSliceError {
 impl From<InvalidSighashTypeError> for SigFromSliceError {
     fn from(err: InvalidSighashTypeError) -> Self { Self::SighashType(err) }
 }
+
+#[cfg(feature = "arbitrary")]
+impl<'a> Arbitrary<'a> for Signature {
+    fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {
+        let arbitrary_bytes: [u8; secp256k1::constants::SCHNORR_SIGNATURE_SIZE] = u.arbitrary()?;
+
+        Ok(Signature {
+            signature: secp256k1::schnorr::Signature::from_slice(&arbitrary_bytes).unwrap(),
+            sighash_type: TapSighashType::arbitrary(u)?,
+        })
+    }
+}