Merge #64: CT descriptor: use hex for single private view keys

81a4a83 CT descriptor: use hex for single private view keys (Leonardo Comandini)

Pull request description:

  Changes related to ElementsProject/ELIPs#9

ACKs for top commit:
  RCasatta:
    ACK 81a4a83 checked that test cases matches the ones in ElementsProject/ELIPs@0ddbaaa
  apoelstra:
    ACK 81a4a83

Tree-SHA512: 3c96fbf6fef8f333457e70da6c1b180dc5df10f473f04317e6c34bc2e453e94ce24355179a3d25adf434a9ee83ab0d9aaa1158398c518472a5d596dca8b34230

Author: apoelstra

src/confidential/mod.rs

@@ -50,7 +50,17 @@ impl fmt::Display for Key {
         match self {
             Key::Slip77(data) => write!(f, "slip77({})", data),
             Key::Bare(pk) => fmt::Display::fmt(pk, f),
-            Key::View(sk) => fmt::Display::fmt(sk, f),
+            Key::View(sk) => {
+                if let DescriptorSecretKey::Single(sk) = sk {
+                    crate::descriptor::maybe_fmt_master_id(f, &sk.origin)?;
+                    for byte in &sk.key.inner.secret_bytes() {
+                        write!(f, "{:02x}", byte)?;
+                    }
+                    Ok(())
+                } else {
+                    fmt::Display::fmt(sk, f)
+                }
+            }
         }
     }
 }
@@ -211,7 +221,7 @@ impl_from_str!(
                     "slip77() must have exactly one argument".to_owned()
                 )),
                 _ => expression::terminal(keyexpr, DescriptorPublicKey::from_str).map(Key::Bare)
-                .or_else(|_| expression::terminal(keyexpr, DescriptorSecretKey::from_str).map(Key::View))?,
+                .or_else(|_| expression::terminal(keyexpr, |s: &str| DescriptorSecretKey::from_str_inner(s, true)).map(Key::View))?,
             },
             descriptor: crate::Descriptor::from_tree(&top.args[1])?,
         })
@@ -420,6 +430,10 @@ mod tests {
                 "ct(pk(02dce16018bbbb8e36de7b394df5b5166e9adb7498be7d881a85a09aeecf76b623),elwpkh(03774eec7a3d550d18e9f89414152025b3b0ad6a342b19481f702d843cff06dfc4))#nvax6rau",
                 "unexpected «pk»",
             ),
+            (
+                "ct(L3jXxwef3fpB7hcrFozcWgHeJCPSAFiZ1Ji2YJMPxceaGvy3PC1q,elwpkh(03774eec7a3d550d18e9f89414152025b3b0ad6a342b19481f702d843cff06dfc4))#gcy6hcfz",
+                "unexpected «Error while parsing xkey.»",
+            ),
         ];
 
         /*
@@ -470,6 +484,26 @@ mod tests {
         test.check(&secp);
     }
 
+    #[test]
+    fn view_single_key_descriptor() {
+        let secp = secp256k1_zkp::Secp256k1::new();
+        let view_key = "c25deb86fa11e49d651d7eae27c220ef930fbd86ea023eebfa73e54875647963";
+        let ct_key = "0286fc9a38e765d955e9b0bcc18fa9ae81b0c893e2dd1ef5542a9c73780a086b90";
+        let pk = "021a8fb6bd5a653b021b98a2a785725b8ddacfe3687bc043aa7f4d25d3a48d40b5";
+        let addr_conf = "el1qq265u4g3k3m3qpyxjwpdrtnm293wuxgvs9xzmzcs2ck0mv5rx23w4d7xfsednsmmxrszfe7s9rs0c6cvf3dfyqwa4jj40uffq";
+        let addr_unconf = "ert1qklrycvkecdanpcpyulgz3c8udvxyck5jkzxddw";
+
+        for desc_str in [
+            format!("ct({view_key},elwpkh({pk}))#c2kx9zll"),
+            format!("ct({ct_key},elwpkh({pk}))#m5mvyh29"),
+        ] {
+            let desc = Descriptor::<DefiniteDescriptorKey>::from_str(&desc_str).unwrap();
+            assert_eq!(desc.to_string(), desc_str);
+            assert_eq!(addr_conf, &desc.address(&secp, &elements::AddressParams::ELEMENTS).unwrap().to_string());
+            assert_eq!(addr_unconf, &desc.unconfidential_address(&elements::AddressParams::ELEMENTS).unwrap().to_string());
+        }
+    }
+
     #[test]
     fn descriptor_wildcard() {
         let secp = secp256k1_zkp::Secp256k1::new();

src/descriptor/key.rs

@@ -7,6 +7,7 @@ use std::{error, fmt};
 use bitcoin::hash_types::XpubIdentifier;
 use bitcoin::{self, bip32};
 use elements::hashes::{hash160, ripemd160, sha256, Hash, HashEngine};
+use elements::hex::FromHex;
 use elements::secp256k1_zkp::{Secp256k1, Signing, Verification};
 
 #[cfg(feature = "serde")]
@@ -382,7 +383,7 @@ impl DescriptorSecretKey {
 }
 
 /// Writes the fingerprint of the origin, if there is one.
-fn maybe_fmt_master_id(
+pub(crate) fn maybe_fmt_master_id(
     f: &mut fmt::Formatter<'_>,
     origin: &Option<(bip32::Fingerprint, bip32::DerivationPath)>,
 ) -> fmt::Result {
@@ -691,13 +692,21 @@ impl DescriptorPublicKey {
     }
 }
 
-impl FromStr for DescriptorSecretKey {
-    type Err = DescriptorKeyParseError;
-
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
+impl DescriptorSecretKey {
+    pub(crate) fn from_str_inner(s: &str, single_hex: bool) -> Result<Self, DescriptorKeyParseError> {
         let (key_part, origin) = parse_key_origin(s)?;
 
-        if key_part.len() <= 52 {
+        if single_hex && key_part.len() == 64 {
+            let bytes = Vec::<u8>::from_hex(key_part)
+                .map_err(|_| DescriptorKeyParseError("Error while parsing a HEX private key"))?;
+            let network = bitcoin::network::constants::Network::Bitcoin; // Use any network
+            let sk = bitcoin::PrivateKey::from_slice(&bytes, network)
+                .map_err(|_| DescriptorKeyParseError("Error while parsing a HEX private key"))?;
+            Ok(DescriptorSecretKey::Single(SinglePriv {
+                key: sk,
+                origin: None,
+            }))
+        } else if !single_hex && key_part.len() <= 52 {
             let sk = bitcoin::PrivateKey::from_str(key_part)
                 .map_err(|_| DescriptorKeyParseError("Error while parsing a WIF private key"))?;
             Ok(DescriptorSecretKey::Single(SinglePriv {
@@ -726,6 +735,14 @@ impl FromStr for DescriptorSecretKey {
     }
 }
 
+impl FromStr for DescriptorSecretKey {
+    type Err = DescriptorKeyParseError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Self::from_str_inner(s, false)
+    }
+}
+
 // Parse the origin information part of a descriptor key.
 fn parse_key_origin(s: &str) -> Result<(&str, Option<bip32::KeySource>), DescriptorKeyParseError> {
     for ch in s.as_bytes() {

src/descriptor/mod.rs

@@ -55,6 +55,7 @@ pub use self::key::{
     DescriptorMultiXKey, DescriptorPublicKey, DescriptorSecretKey, DescriptorXKey, InnerXKey,
     SinglePriv, SinglePub, SinglePubKey, Wildcard,
 };
+pub(crate) use self::key::maybe_fmt_master_id;
 pub use self::tr::{TapTree, Tr, TapLeafScript};
 /// Alias type for a map of public key to secret key
 ///