ecdsa.rs

// Rust Bitcoin Library
// Written in 2014 by
//     Andrew Poelstra <apoelstra@wpsoftware.net>
// To the extent possible under law, the author(s) have dedicated all
// copyright and related and neighboring rights to this software to
// the public domain worldwide. This software is distributed without
// any warranty.
//
// You should have received a copy of the CC0 Public Domain Dedication
// along with this software.
// If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
//

//! ECDSA Bitcoin keys.
//!
//! This module provides ECDSA keys used in Bitcoin that can be roundtrip
//! (de)serialized.
//!

use prelude::*;

use core::{ops, str::FromStr, iter};
use core::fmt::{self, Write as _fmtWrite};
use io;

use secp256k1::{self, Secp256k1};
use network::constants::Network;
use hashes::{Hash, hash160, hex};
use hashes::hex::FromHex;
use hash_types::{PubkeyHash, WPubkeyHash};
use util::base58;
use util::key::Error;
use blockdata::transaction::{EcdsaSigHashType, NonStandardSigHashType};


/// A Bitcoin ECDSA public key
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct PublicKey {
    /// Whether this public key should be serialized as compressed
    pub compressed: bool,
    /// The actual ECDSA key
    pub inner: secp256k1::PublicKey,
}

impl PublicKey {
    /// Constructs compressed ECDSA public key from the provided generic Secp256k1 public key
    pub fn new(key: secp256k1::PublicKey) -> PublicKey {
        PublicKey {
            compressed: true,
            inner: key,
        }
    }

    /// Constructs uncompressed (legacy) ECDSA public key from the provided generic Secp256k1
    /// public key
    pub fn new_uncompressed(key: secp256k1::PublicKey) -> PublicKey {
        PublicKey {
            compressed: false,
            inner: key,
        }
    }

    /// Returns bitcoin 160-bit hash of the public key
    pub fn pubkey_hash(&self) -> PubkeyHash {
        if self.compressed {
            PubkeyHash::hash(&self.inner.serialize())
        } else {
            PubkeyHash::hash(&self.inner.serialize_uncompressed())
        }
    }

    /// Returns bitcoin 160-bit hash of the public key for witness program
    pub fn wpubkey_hash(&self) -> Option<WPubkeyHash> {
        if self.compressed {
            Some(WPubkeyHash::from_inner(
                hash160::Hash::hash(&self.inner.serialize()).into_inner()
            ))
        } else {
            // We can't create witness pubkey hashes for an uncompressed
            // public keys
            None
        }
    }

    /// Write the public key into a writer
    pub fn write_into<W: io::Write>(&self, mut writer: W) -> Result<(), io::Error> {
        if self.compressed {
            writer.write_all(&self.inner.serialize())
        } else {
            writer.write_all(&self.inner.serialize_uncompressed())
        }
    }

    /// Read the public key from a reader
    ///
    /// This internally reads the first byte before reading the rest, so
    /// use of a `BufReader` is recommended.
    pub fn read_from<R: io::Read>(mut reader: R) -> Result<Self, io::Error> {
        let mut bytes = [0; 65];

        reader.read_exact(&mut bytes[0..1])?;
        let bytes = if bytes[0] < 4 {
            &mut bytes[..33]
        } else {
            &mut bytes[..65]
        };

        reader.read_exact(&mut bytes[1..])?;
        Self::from_slice(bytes).map_err(|e|{
            // Need a static string for core2
            #[cfg(feature = "std")]
            let reason = e;
            #[cfg(not(feature = "std"))]
            let reason = match e {
                Error::Base58(_) => "base58 error",
                Error::Secp256k1(_) => "secp256k1 error",
            };
            io::Error::new(io::ErrorKind::InvalidData, reason)
        })
    }

    /// Serialize the public key to bytes
    pub fn to_bytes(&self) -> Vec<u8> {
        let mut buf = Vec::new();
        self.write_into(&mut buf).expect("vecs don't error");
        buf
    }

    /// Deserialize a public key from a slice
    pub fn from_slice(data: &[u8]) -> Result<PublicKey, Error> {
        let compressed: bool = match data.len() {
            33 => true,
            65 => false,
            len =>  { return Err(base58::Error::InvalidLength(len).into()); },
        };

        Ok(PublicKey {
            compressed,
            inner: secp256k1::PublicKey::from_slice(data)?,
        })
    }

    /// Computes the public key as supposed to be used with this secret
    pub fn from_private_key<C: secp256k1::Signing>(secp: &Secp256k1<C>, sk: &PrivateKey) -> PublicKey {
        sk.public_key(secp)
    }
}

impl fmt::Display for PublicKey {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        if self.compressed {
            for ch in &self.inner.serialize()[..] {
                write!(f, "{:02x}", ch)?;
            }
        } else {
            for ch in &self.inner.serialize_uncompressed()[..] {
                write!(f, "{:02x}", ch)?;
            }
        }
        Ok(())
    }
}

impl FromStr for PublicKey {
    type Err = Error;
    fn from_str(s: &str) -> Result<PublicKey, Error> {
        let key = secp256k1::PublicKey::from_str(s)?;
        Ok(PublicKey {
            inner: key,
            compressed: s.len() == 66
        })
    }
}

/// A Bitcoin ECDSA private key
#[derive(Copy, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "std", derive(Debug))]
pub struct PrivateKey {
    /// Whether this private key should be serialized as compressed
    pub compressed: bool,
    /// The network on which this key should be used
    pub network: Network,
    /// The actual ECDSA key
    pub inner: secp256k1::SecretKey,
}

impl PrivateKey {
    /// Constructs compressed ECDSA private key from the provided generic Secp256k1 private key
    /// and the specified network
    pub fn new(key: secp256k1::SecretKey, network: Network) -> PrivateKey {
        PrivateKey {
            compressed: true,
            network,
            inner: key,
        }
    }

    /// Constructs uncompressed (legacy) ECDSA private key from the provided generic Secp256k1
    /// private key and the specified network
    pub fn new_uncompressed(key: secp256k1::SecretKey, network: Network) -> PrivateKey {
        PrivateKey {
            compressed: false,
            network,
            inner: key,
        }
    }

    /// Creates a public key from this private key
    pub fn public_key<C: secp256k1::Signing>(&self, secp: &Secp256k1<C>) -> PublicKey {
        PublicKey {
            compressed: self.compressed,
            inner: secp256k1::PublicKey::from_secret_key(secp, &self.inner)
        }
    }

    /// Serialize the private key to bytes
    pub fn to_bytes(&self) -> Vec<u8> {
        self.inner[..].to_vec()
    }

    /// Deserialize a private key from a slice
    pub fn from_slice(data: &[u8], network: Network) -> Result<PrivateKey, Error> {
        Ok(PrivateKey::new(
            secp256k1::SecretKey::from_slice(data)?,
            network,
        ))
    }

    /// Format the private key to WIF format.
    pub fn fmt_wif(&self, fmt: &mut dyn fmt::Write) -> fmt::Result {
        let mut ret = [0; 34];
        ret[0] = match self.network {
            Network::Bitcoin => 128,
            Network::Testnet | Network::Signet | Network::Regtest => 239,
        };
        ret[1..33].copy_from_slice(&self.inner[..]);
        let privkey = if self.compressed {
            ret[33] = 1;
            base58::check_encode_slice(&ret[..])
        } else {
            base58::check_encode_slice(&ret[..33])
        };
        fmt.write_str(&privkey)
    }

    /// Get WIF encoding of this private key.
    pub fn to_wif(&self) -> String {
        let mut buf = String::new();
        buf.write_fmt(format_args!("{}", self)).unwrap();
        buf.shrink_to_fit();
        buf
    }

    /// Parse WIF encoded private key.
    pub fn from_wif(wif: &str) -> Result<PrivateKey, Error> {
        let data = base58::from_check(wif)?;

        let compressed = match data.len() {
            33 => false,
            34 => true,
            _ => { return Err(Error::Base58(base58::Error::InvalidLength(data.len()))); }
        };

        let network = match data[0] {
            128 => Network::Bitcoin,
            239 => Network::Testnet,
            x   => { return Err(Error::Base58(base58::Error::InvalidAddressVersion(x))); }
        };

        Ok(PrivateKey {
            compressed,
            network,
            inner: secp256k1::SecretKey::from_slice(&data[1..33])?,
        })
    }
}

impl fmt::Display for PrivateKey {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.fmt_wif(f)
    }
}

#[cfg(not(feature = "std"))]
impl fmt::Debug for PrivateKey {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "[private key data]")
    }
}

impl FromStr for PrivateKey {
    type Err = Error;
    fn from_str(s: &str) -> Result<PrivateKey, Error> {
        PrivateKey::from_wif(s)
    }
}

impl ops::Index<ops::RangeFull> for PrivateKey {
    type Output = [u8];
    fn index(&self, _: ops::RangeFull) -> &[u8] {
        &self.inner[..]
    }
}

#[cfg(feature = "serde")]
#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
impl ::serde::Serialize for PrivateKey {
    fn serialize<S: ::serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
        s.collect_str(self)
    }
}

#[cfg(feature = "serde")]
#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
impl<'de> ::serde::Deserialize<'de> for PrivateKey {
    fn deserialize<D: ::serde::Deserializer<'de>>(d: D) -> Result<PrivateKey, D::Error> {
        struct WifVisitor;

        impl<'de> ::serde::de::Visitor<'de> for WifVisitor {
            type Value = PrivateKey;

            fn expecting(&self, formatter: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                formatter.write_str("an ASCII WIF string")
            }

            fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
            where
                E: ::serde::de::Error,
            {
                if let Ok(s) = ::core::str::from_utf8(v) {
                    PrivateKey::from_str(s).map_err(E::custom)
                } else {
                    Err(E::invalid_value(::serde::de::Unexpected::Bytes(v), &self))
                }
            }

            fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
            where
                E: ::serde::de::Error,
            {
                PrivateKey::from_str(v).map_err(E::custom)
            }
        }

        d.deserialize_str(WifVisitor)
    }
}

#[cfg(feature = "serde")]
#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
impl ::serde::Serialize for PublicKey {
    fn serialize<S: ::serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
        if s.is_human_readable() {
            s.collect_str(self)
        } else {
            if self.compressed {
                s.serialize_bytes(&self.inner.serialize()[..])
            } else {
                s.serialize_bytes(&self.inner.serialize_uncompressed()[..])
            }
        }
    }
}

#[cfg(feature = "serde")]
#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
impl<'de> ::serde::Deserialize<'de> for PublicKey {
    fn deserialize<D: ::serde::Deserializer<'de>>(d: D) -> Result<PublicKey, D::Error> {
        if d.is_human_readable() {
            struct HexVisitor;

            impl<'de> ::serde::de::Visitor<'de> for HexVisitor {
                type Value = PublicKey;

                fn expecting(&self, formatter: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                    formatter.write_str("an ASCII hex string")
                }

                fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
                where
                    E: ::serde::de::Error,
                {
                    if let Ok(hex) = ::core::str::from_utf8(v) {
                        PublicKey::from_str(hex).map_err(E::custom)
                    } else {
                        Err(E::invalid_value(::serde::de::Unexpected::Bytes(v), &self))
                    }
                }

                fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
                where
                    E: ::serde::de::Error,
                {
                    PublicKey::from_str(v).map_err(E::custom)
                }
            }
            d.deserialize_str(HexVisitor)
        } else {
            struct BytesVisitor;

            impl<'de> ::serde::de::Visitor<'de> for BytesVisitor {
                type Value = PublicKey;

                fn expecting(&self, formatter: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                    formatter.write_str("a bytestring")
                }

                fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
                where
                    E: ::serde::de::Error,
                {
                    PublicKey::from_slice(v).map_err(E::custom)
                }
            }

            d.deserialize_bytes(BytesVisitor)
        }
    }
}

/// An ECDSA signature with the corresponding hash type.
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub struct EcdsaSig {
    /// The underlying ECDSA Signature
    pub sig: secp256k1::ecdsa::Signature,
    /// The corresponding hash type
    pub hash_ty: EcdsaSigHashType,
}

impl EcdsaSig {
    /// Constructs ECDSA bitcoin signature for [`EcdsaSigHashType::All`]
    pub fn sighash_all(sig: secp256k1::ecdsa::Signature) -> EcdsaSig {
        EcdsaSig {
            sig,
            hash_ty: EcdsaSigHashType::All
        }
    }

    /// Deserialize from slice following the standardness rules for [`EcdsaSigHashType`]
    pub fn from_slice(sl: &[u8]) -> Result<Self, EcdsaSigError> {
        let (hash_ty, sig) = sl.split_last()
            .ok_or(EcdsaSigError::EmptySignature)?;
        let hash_ty = EcdsaSigHashType::from_u32_standard(*hash_ty as u32)
            .map_err(|_| EcdsaSigError::NonStandardSigHashType(*hash_ty as u32))?;
        let sig = secp256k1::ecdsa::Signature::from_der(sig)
            .map_err(EcdsaSigError::Secp256k1)?;
        Ok(EcdsaSig { sig, hash_ty })
    }

    /// Serialize EcdsaSig
    pub fn to_vec(&self) -> Vec<u8> {
        // TODO: add support to serialize to a writer to SerializedSig
        self.sig.serialize_der()
            .iter().map(|x| *x)
            .chain(iter::once(self.hash_ty as u8))
            .collect()
    }
}

impl fmt::Display for EcdsaSig {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        hex::format_hex(&self.sig.serialize_der(), f)?;
        hex::format_hex(&[self.hash_ty as u8], f)
    }
}

impl FromStr for EcdsaSig {
    type Err = EcdsaSigError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let bytes = Vec::from_hex(s)?;
        let (sighash_byte, signature) = bytes.split_last()
            .ok_or(EcdsaSigError::EmptySignature)?;
        Ok(EcdsaSig {
            sig: secp256k1::ecdsa::Signature::from_der(signature)?,
            hash_ty: EcdsaSigHashType::from_u32_standard(*sighash_byte as u32)?
        })
    }
}

/// A key-related error.
#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
pub enum EcdsaSigError {
    /// Hex encoding error
    HexEncoding(hex::Error),
    /// Base58 encoding error
    NonStandardSigHashType(u32),
    /// Empty Signature
    EmptySignature,
    /// secp256k1-related error
    Secp256k1(secp256k1::Error),
}


impl fmt::Display for EcdsaSigError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            EcdsaSigError::NonStandardSigHashType(hash_ty) =>
                write!(f, "Non standard signature hash type {}", hash_ty),
            EcdsaSigError::Secp256k1(ref e) =>
                write!(f, "Invalid Ecdsa signature: {}", e),
            EcdsaSigError::EmptySignature =>
                write!(f, "Empty ECDSA signature"),
            EcdsaSigError::HexEncoding(e) => write!(f, "EcdsaSig hex encoding error: {}", e)
        }
    }
}

#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
impl ::std::error::Error for EcdsaSigError {}

impl From<secp256k1::Error> for EcdsaSigError {
    fn from(e: secp256k1::Error) -> EcdsaSigError {
        EcdsaSigError::Secp256k1(e)
    }
}

impl From<NonStandardSigHashType> for EcdsaSigError {
    fn from(err: NonStandardSigHashType) -> Self {
        EcdsaSigError::NonStandardSigHashType(err.0)
    }
}

impl From<hex::Error> for EcdsaSigError {
    fn from(err: hex::Error) -> Self {
        EcdsaSigError::HexEncoding(err)
    }
}

#[cfg(test)]
mod tests {
    use io;
    use super::{PrivateKey, PublicKey};
    use secp256k1::Secp256k1;
    use std::str::FromStr;
    use hashes::hex::ToHex;
    use network::constants::Network::Testnet;
    use network::constants::Network::Bitcoin;
    use util::address::Address;

    #[test]
    fn test_key_derivation() {
        // testnet compressed
        let sk = PrivateKey::from_wif("cVt4o7BGAig1UXywgGSmARhxMdzP5qvQsxKkSsc1XEkw3tDTQFpy").unwrap();
        assert_eq!(sk.network, Testnet);
        assert_eq!(sk.compressed, true);
        assert_eq!(&sk.to_wif(), "cVt4o7BGAig1UXywgGSmARhxMdzP5qvQsxKkSsc1XEkw3tDTQFpy");

        let secp = Secp256k1::new();
        let pk = Address::p2pkh(&sk.public_key(&secp), sk.network);
        assert_eq!(&pk.to_string(), "mqwpxxvfv3QbM8PU8uBx2jaNt9btQqvQNx");

        // test string conversion
        assert_eq!(&sk.to_string(), "cVt4o7BGAig1UXywgGSmARhxMdzP5qvQsxKkSsc1XEkw3tDTQFpy");
        let sk_str =
            PrivateKey::from_str("cVt4o7BGAig1UXywgGSmARhxMdzP5qvQsxKkSsc1XEkw3tDTQFpy").unwrap();
        assert_eq!(&sk.to_wif(), &sk_str.to_wif());

        // mainnet uncompressed
        let sk = PrivateKey::from_wif("5JYkZjmN7PVMjJUfJWfRFwtuXTGB439XV6faajeHPAM9Z2PT2R3").unwrap();
        assert_eq!(sk.network, Bitcoin);
        assert_eq!(sk.compressed, false);
        assert_eq!(&sk.to_wif(), "5JYkZjmN7PVMjJUfJWfRFwtuXTGB439XV6faajeHPAM9Z2PT2R3");

        let secp = Secp256k1::new();
        let mut pk = sk.public_key(&secp);
        assert_eq!(pk.compressed, false);
        assert_eq!(&pk.to_string(), "042e58afe51f9ed8ad3cc7897f634d881fdbe49a81564629ded8156bebd2ffd1af191923a2964c177f5b5923ae500fca49e99492d534aa3759d6b25a8bc971b133");
        assert_eq!(pk, PublicKey::from_str("042e58afe51f9ed8ad3cc7897f634d881fdbe49a81564629ded8156bebd2ffd1af191923a2964c177f5b5923ae500fca49e99492d534aa3759d6b25a8bc971b133").unwrap());
        let addr = Address::p2pkh(&pk, sk.network);
        assert_eq!(&addr.to_string(), "1GhQvF6dL8xa6wBxLnWmHcQsurx9RxiMc8");
        pk.compressed = true;
        assert_eq!(&pk.to_string(), "032e58afe51f9ed8ad3cc7897f634d881fdbe49a81564629ded8156bebd2ffd1af");
        assert_eq!(pk, PublicKey::from_str("032e58afe51f9ed8ad3cc7897f634d881fdbe49a81564629ded8156bebd2ffd1af").unwrap());
    }

    #[test]
    fn test_pubkey_hash() {
        let pk = PublicKey::from_str("032e58afe51f9ed8ad3cc7897f634d881fdbe49a81564629ded8156bebd2ffd1af").unwrap();
        let upk = PublicKey::from_str("042e58afe51f9ed8ad3cc7897f634d881fdbe49a81564629ded8156bebd2ffd1af191923a2964c177f5b5923ae500fca49e99492d534aa3759d6b25a8bc971b133").unwrap();
        assert_eq!(pk.pubkey_hash().to_hex(), "9511aa27ef39bbfa4e4f3dd15f4d66ea57f475b4");
        assert_eq!(upk.pubkey_hash().to_hex(), "ac2e7daf42d2c97418fd9f78af2de552bb9c6a7a");
    }

    #[test]
    fn test_wpubkey_hash() {
        let pk = PublicKey::from_str("032e58afe51f9ed8ad3cc7897f634d881fdbe49a81564629ded8156bebd2ffd1af").unwrap();
        let upk = PublicKey::from_str("042e58afe51f9ed8ad3cc7897f634d881fdbe49a81564629ded8156bebd2ffd1af191923a2964c177f5b5923ae500fca49e99492d534aa3759d6b25a8bc971b133").unwrap();
        assert_eq!(pk.wpubkey_hash().unwrap().to_hex(), "9511aa27ef39bbfa4e4f3dd15f4d66ea57f475b4");
        assert_eq!(upk.wpubkey_hash(), None);
    }

    #[cfg(feature = "serde")]
    #[test]
    fn test_key_serde() {
        use serde_test::{Configure, Token, assert_tokens};

        static KEY_WIF: &'static str = "cVt4o7BGAig1UXywgGSmARhxMdzP5qvQsxKkSsc1XEkw3tDTQFpy";
        static PK_STR: &'static str = "039b6347398505f5ec93826dc61c19f47c66c0283ee9be980e29ce325a0f4679ef";
        static PK_STR_U: &'static str = "\
            04\
            9b6347398505f5ec93826dc61c19f47c66c0283ee9be980e29ce325a0f4679ef\
            87288ed73ce47fc4f5c79d19ebfa57da7cff3aff6e819e4ee971d86b5e61875d\
        ";
        static PK_BYTES: [u8; 33] = [
            0x03,
            0x9b, 0x63, 0x47, 0x39, 0x85, 0x05, 0xf5, 0xec,
            0x93, 0x82, 0x6d, 0xc6, 0x1c, 0x19, 0xf4, 0x7c,
            0x66, 0xc0, 0x28, 0x3e, 0xe9, 0xbe, 0x98, 0x0e,
            0x29, 0xce, 0x32, 0x5a, 0x0f, 0x46, 0x79, 0xef,
        ];
        static PK_BYTES_U: [u8; 65] = [
            0x04,
            0x9b, 0x63, 0x47, 0x39, 0x85, 0x05, 0xf5, 0xec,
            0x93, 0x82, 0x6d, 0xc6, 0x1c, 0x19, 0xf4, 0x7c,
            0x66, 0xc0, 0x28, 0x3e, 0xe9, 0xbe, 0x98, 0x0e,
            0x29, 0xce, 0x32, 0x5a, 0x0f, 0x46, 0x79, 0xef,
            0x87, 0x28, 0x8e, 0xd7, 0x3c, 0xe4, 0x7f, 0xc4,
            0xf5, 0xc7, 0x9d, 0x19, 0xeb, 0xfa, 0x57, 0xda,
            0x7c, 0xff, 0x3a, 0xff, 0x6e, 0x81, 0x9e, 0x4e,
            0xe9, 0x71, 0xd8, 0x6b, 0x5e, 0x61, 0x87, 0x5d,
        ];

        let s = Secp256k1::new();
        let sk = PrivateKey::from_str(&KEY_WIF).unwrap();
        let pk = PublicKey::from_private_key(&s, &sk);
        let pk_u = PublicKey {
            inner: pk.inner,
            compressed: false,
        };

        assert_tokens(&sk, &[Token::BorrowedStr(KEY_WIF)]);
        assert_tokens(&pk.compact(), &[Token::BorrowedBytes(&PK_BYTES[..])]);
        assert_tokens(&pk.readable(), &[Token::BorrowedStr(PK_STR)]);
        assert_tokens(&pk_u.compact(), &[Token::BorrowedBytes(&PK_BYTES_U[..])]);
        assert_tokens(&pk_u.readable(), &[Token::BorrowedStr(PK_STR_U)]);
    }

    fn random_key(mut seed: u8) -> PublicKey {
        loop {
            let mut data = [0; 65];
            for byte in &mut data[..] {
                *byte = seed;
                // totally a rng
                seed = seed.wrapping_mul(41).wrapping_add(43);
            }
            if data[0] % 2 == 0 {
                data[0] = 4;
                if let Ok(key) = PublicKey::from_slice(&data[..]) {
                    return key;
                }
            } else {
                data[0] = 2 + (data[0] >> 7);
                if let Ok(key) = PublicKey::from_slice(&data[..33]) {
                    return key;
                }
            }
        }
    }

    #[test]
    fn pubkey_read_write() {
        const N_KEYS: usize = 20;
        let keys: Vec<_> = (0..N_KEYS).map(|i| random_key(i as u8)).collect();

        let mut v = vec![];
        for k in &keys {
            k.write_into(&mut v).expect("writing into vec");
        }

        let mut dec_keys = vec![];
        let mut cursor = io::Cursor::new(&v);
        for _ in 0..N_KEYS {
            dec_keys.push(PublicKey::read_from(&mut cursor).expect("reading from vec"));
        }

        assert_eq!(keys, dec_keys);

        // sanity checks
        assert!(PublicKey::read_from(&mut cursor).is_err());
        assert!(PublicKey::read_from(io::Cursor::new(&[])).is_err());
        assert!(PublicKey::read_from(io::Cursor::new(&[0; 33][..])).is_err());
        assert!(PublicKey::read_from(io::Cursor::new(&[2; 32][..])).is_err());
        assert!(PublicKey::read_from(io::Cursor::new(&[0; 65][..])).is_err());
        assert!(PublicKey::read_from(io::Cursor::new(&[4; 64][..])).is_err());
    }
}