Merge pull request #197 from darosior/descriptor_checksum

Descriptor checksum

Author: apoelstra

examples/htlc.rs

@@ -41,7 +41,7 @@ fn main() {
     assert!(htlc_descriptor.sanity_check().is_ok());
     assert_eq!(
         format!("{}", htlc_descriptor),
-        "wsh(andor(pk(022222222222222222222222222222222222222222222222222222222222222222),sha256(1111111111111111111111111111111111111111111111111111111111111111),and_v(v:pkh(51814f108670aced2d77c1805ddd6634bc9d4731),older(4444))))"
+        "wsh(andor(pk(022222222222222222222222222222222222222222222222222222222222222222),sha256(1111111111111111111111111111111111111111111111111111111111111111),and_v(v:pkh(51814f108670aced2d77c1805ddd6634bc9d4731),older(4444))))#s0qq76ng"
     );
 
     assert_eq!(

fuzz/fuzz_targets/roundtrip_descriptor.rs

@@ -8,7 +8,7 @@ use std::str::FromStr;
 fn do_test(data: &[u8]) {
     let s = String::from_utf8_lossy(data);
     if let Ok(desc) = Descriptor::<DummyKey>::from_str(&s) {
-        let output = desc.to_string();
+        let output = format!("{:?}", desc);
 
         let multi_wrap_pk_re = Regex::new("([a-z]+)c:pk_k\\(").unwrap();
         let multi_wrap_pkh_re = Regex::new("([a-z]+)c:pk_h\\(").unwrap();

src/descriptor/checksum.rs

@@ -0,0 +1,126 @@
+//! Descriptor checksum
+//!
+//! This module contains a re-implementation of the function used by Bitcoin Core to calculate the
+//! checksum of a descriptor
+
+use std::iter::FromIterator;
+
+use Error;
+
+const INPUT_CHARSET: &str =  "0123456789()[],'/*abcdefgh@:$%{}IJKLMNOPQRSTUVWXYZ&+-.;<=>?!^_|~ijklmnopqrstuvwxyzABCDEFGH`#\"\\ ";
+const CHECKSUM_CHARSET: &str = "qpzry9x8gf2tvdw0s3jn54khce6mua7l";
+
+fn poly_mod(mut c: u64, val: u64) -> u64 {
+    let c0 = c >> 35;
+
+    c = ((c & 0x7ffffffff) << 5) ^ val;
+    if c0 & 1 > 0 {
+        c ^= 0xf5dee51989
+    };
+    if c0 & 2 > 0 {
+        c ^= 0xa9fdca3312
+    };
+    if c0 & 4 > 0 {
+        c ^= 0x1bab10e32d
+    };
+    if c0 & 8 > 0 {
+        c ^= 0x3706b1677a
+    };
+    if c0 & 16 > 0 {
+        c ^= 0x644d626ffd
+    };
+
+    c
+}
+
+/// Compute the checksum of a descriptor
+pub fn desc_checksum(desc: &str) -> Result<String, Error> {
+    let mut c = 1;
+    let mut cls = 0;
+    let mut clscount = 0;
+
+    for ch in desc.chars() {
+        let pos = INPUT_CHARSET.find(ch).ok_or(Error::BadDescriptor(format!(
+            "Invalid character in checksum: '{}'",
+            ch
+        )))? as u64;
+        c = poly_mod(c, pos & 31);
+        cls = cls * 3 + (pos >> 5);
+        clscount += 1;
+        if clscount == 3 {
+            c = poly_mod(c, cls);
+            cls = 0;
+            clscount = 0;
+        }
+    }
+    if clscount > 0 {
+        c = poly_mod(c, cls);
+    }
+    (0..8).for_each(|_| c = poly_mod(c, 0));
+    c ^= 1;
+
+    let mut chars = Vec::with_capacity(8);
+    for j in 0..8 {
+        chars.push(
+            CHECKSUM_CHARSET
+                .chars()
+                .nth(((c >> (5 * (7 - j))) & 31) as usize)
+                .unwrap(),
+        );
+    }
+
+    Ok(String::from_iter(chars))
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use std::str;
+
+    macro_rules! check_expected {
+        ($desc: expr, $checksum: expr) => {
+            assert_eq!(desc_checksum($desc).unwrap(), $checksum);
+        };
+    }
+
+    #[test]
+    fn test_valid_descriptor_checksum() {
+        check_expected!(
+            "wpkh(tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcLNfjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/2/*)",
+            "tqz0nc62"
+        );
+        check_expected!(
+            "pkh(tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/44'/1'/0'/0/*)",
+            "lasegmfs"
+        );
+
+        // https://github.com/bitcoin/bitcoin/blob/7ae86b3c6845873ca96650fc69beb4ae5285c801/src/test/descriptor_tests.cpp#L352-L354
+        check_expected!(
+            "sh(multi(2,[00000000/111'/222]xprvA1RpRA33e1JQ7ifknakTFpgNXPmW2YvmhqLQYMmrj4xJXXWYpDPS3xz7iAxn8L39njGVyuoseXzU6rcxFLJ8HFsTjSyQbLYnMpCqE2VbFWc,xprv9uPDJpEQgRQfDcW7BkF7eTya6RPxXeJCqCJGHuCJ4GiRVLzkTXBAJMu2qaMWPrS7AANYqdq6vcBcBUdJCVVFceUvJFjaPdGZ2y9WACViL4L/0))",
+            "ggrsrxfy"
+        );
+        check_expected!(
+            "sh(multi(2,[00000000/111'/222]xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL,xpub68NZiKmJWnxxS6aaHmn81bvJeTESw724CRDs6HbuccFQN9Ku14VQrADWgqbhhTHBaohPX4CjNLf9fq9MYo6oDaPPLPxSb7gwQN3ih19Zm4Y/0))",
+            "tjg09x5t"
+        );
+    }
+
+    #[test]
+    fn test_desc_checksum_invalid_character() {
+        let sparkle_heart = vec![240, 159, 146, 150];
+        let sparkle_heart = str::from_utf8(&sparkle_heart)
+            .unwrap()
+            .chars()
+            .next()
+            .unwrap();
+        let invalid_desc = format!("wpkh(tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcL{}fjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/2/*)", sparkle_heart);
+
+        assert_eq!(
+            desc_checksum(&invalid_desc).err().unwrap().to_string(),
+            format!(
+                "Invalid descriptor: Invalid character in checksum: '{}'",
+                sparkle_heart
+            )
+        );
+    }
+}