silent payments: file-based key import/export #56
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,7 @@ | ||
| use std::{io, path::Path}; | ||
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| pub trait FileExt: Sized { | ||
| type Error: From<io::Error>; | ||
| fn save(&self, path: &Path) -> Result<(), Self::Error>; | ||
| fn load(path: &Path) -> Result<Self, Self::Error>; | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1 +1,2 @@ | ||
| pub mod io; | ||
| pub mod silentpayments; |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,236 @@ | ||
| use std::{ | ||
| fs, | ||
| io::{self, Write}, | ||
| path::Path, | ||
| }; | ||
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| use bitcoin::secp256k1::{self, Secp256k1, SecretKey, XOnlyPublicKey}; | ||
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| use crate::io::FileExt; | ||
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| const MAGIC: &[u8; 4] = b"SPKF"; | ||
| const KEY_LEN: usize = 32; | ||
| const TAG_LEN: usize = 1; | ||
| const FILE_LEN: usize = MAGIC.len() + KEY_LEN + TAG_LEN + KEY_LEN; | ||
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| const SPEND_TAG_SECRET: u8 = 0; | ||
| const SPEND_TAG_XONLY_PUB: u8 = 1; | ||
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| /// `Secret` for software wallets. `XOnlyPublic` for hardware-signer / watch-only. | ||
| #[derive(Debug, Clone, Copy, PartialEq, Eq)] | ||
| pub enum SpendKey { | ||
| Secret(SecretKey), | ||
| XOnlyPublic(XOnlyPublicKey), | ||
| } | ||
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| impl SpendKey { | ||
| pub fn xonly(&self) -> XOnlyPublicKey { | ||
| match self { | ||
| SpendKey::Secret(sk) => { | ||
| let secp = Secp256k1::signing_only(); | ||
| sk.public_key(&secp).x_only_public_key().0 | ||
| } | ||
| SpendKey::XOnlyPublic(pk) => *pk, | ||
| } | ||
| } | ||
| } | ||
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| /// On-disk format: 4-byte magic `SPKF` (Silent Payment Key File), 32-byte scan | ||
| /// secret, 1-byte spend tag, 32-byte spend material. 69 bytes total. | ||
| #[derive(Debug, Clone, Copy, PartialEq, Eq)] | ||
| pub struct SilentPaymentKeysFile { | ||
| pub scan_key: SecretKey, | ||
| pub spend: SpendKey, | ||
| } | ||
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| #[derive(Debug)] | ||
| pub enum KeysFileError { | ||
| Io(io::Error), | ||
| BadMagic, | ||
| WrongLength { expected: usize, actual: usize }, | ||
| UnknownSpendTag(u8), | ||
| InvalidKey(secp256k1::Error), | ||
| } | ||
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| impl std::fmt::Display for KeysFileError { | ||
| fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { | ||
| match self { | ||
| KeysFileError::Io(e) => write!(f, "i/o error: {e}"), | ||
| KeysFileError::BadMagic => write!(f, "bad magic: not a silent payments keys file"), | ||
| KeysFileError::WrongLength { expected, actual } => write!( | ||
| f, | ||
| "wrong file length: expected {expected} bytes, got {actual}" | ||
| ), | ||
| KeysFileError::UnknownSpendTag(t) => write!(f, "unknown spend tag: {t}"), | ||
| KeysFileError::InvalidKey(e) => write!(f, "invalid key: {e}"), | ||
| } | ||
| } | ||
| } | ||
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| impl std::error::Error for KeysFileError {} | ||
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| impl From<io::Error> for KeysFileError { | ||
| fn from(e: io::Error) -> Self { | ||
| KeysFileError::Io(e) | ||
| } | ||
| } | ||
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| impl From<secp256k1::Error> for KeysFileError { | ||
| fn from(e: secp256k1::Error) -> Self { | ||
| KeysFileError::InvalidKey(e) | ||
| } | ||
| } | ||
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| impl SilentPaymentKeysFile { | ||
| pub fn new(scan_key: SecretKey, spend: SpendKey) -> Self { | ||
| Self { scan_key, spend } | ||
| } | ||
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| pub fn spend_xonly(&self) -> XOnlyPublicKey { | ||
| self.spend.xonly() | ||
| } | ||
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| pub fn to_bytes(&self) -> [u8; FILE_LEN] { | ||
| let mut buf = [0u8; FILE_LEN]; | ||
| let mut off = 0; | ||
| buf[off..off + MAGIC.len()].copy_from_slice(MAGIC); | ||
| off += MAGIC.len(); | ||
| buf[off..off + KEY_LEN].copy_from_slice(&self.scan_key.secret_bytes()); | ||
| off += KEY_LEN; | ||
| match &self.spend { | ||
| SpendKey::Secret(sk) => { | ||
| buf[off] = SPEND_TAG_SECRET; | ||
| buf[off + TAG_LEN..].copy_from_slice(&sk.secret_bytes()); | ||
| } | ||
| SpendKey::XOnlyPublic(pk) => { | ||
| buf[off] = SPEND_TAG_XONLY_PUB; | ||
| buf[off + TAG_LEN..].copy_from_slice(&pk.serialize()); | ||
| } | ||
| } | ||
| buf | ||
| } | ||
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| pub fn from_bytes(bytes: &[u8]) -> Result<Self, KeysFileError> { | ||
| if bytes.len() != FILE_LEN { | ||
| return Err(KeysFileError::WrongLength { | ||
| expected: FILE_LEN, | ||
| actual: bytes.len(), | ||
| }); | ||
| } | ||
| let body = bytes | ||
| .strip_prefix(MAGIC.as_slice()) | ||
| .ok_or(KeysFileError::BadMagic)?; | ||
| let scan_key = SecretKey::from_slice(&body[..KEY_LEN])?; | ||
| let tag = body[KEY_LEN]; | ||
| let spend_bytes = &body[KEY_LEN + TAG_LEN..]; | ||
| let spend = match tag { | ||
| SPEND_TAG_SECRET => SpendKey::Secret(SecretKey::from_slice(spend_bytes)?), | ||
| SPEND_TAG_XONLY_PUB => SpendKey::XOnlyPublic(XOnlyPublicKey::from_slice(spend_bytes)?), | ||
| other => return Err(KeysFileError::UnknownSpendTag(other)), | ||
| }; | ||
| Ok(Self { scan_key, spend }) | ||
| } | ||
| } | ||
|
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| impl FileExt for SilentPaymentKeysFile { | ||
| type Error = KeysFileError; | ||
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| /// Refuses to overwrite (`AlreadyExists`). | ||
| fn save(&self, path: &Path) -> Result<(), Self::Error> { | ||
| let mut file = fs::File::create_new(path)?; | ||
| file.write_all(&self.to_bytes())?; | ||
| Ok(()) | ||
| } | ||
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| fn load(path: &Path) -> Result<Self, Self::Error> { | ||
| let bytes = fs::read(path)?; | ||
| Self::from_bytes(&bytes) | ||
| } | ||
| } | ||
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| #[cfg(test)] | ||
| mod tests { | ||
| use super::*; | ||
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| fn test_keys() -> (SecretKey, SecretKey) { | ||
| let scan = SecretKey::from_slice(&[1u8; 32]).expect("valid scan key"); | ||
| let spend = SecretKey::from_slice(&[2u8; 32]).expect("valid spend key"); | ||
| (scan, spend) | ||
| } | ||
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| fn xonly_from(sk: SecretKey) -> XOnlyPublicKey { | ||
| sk.public_key(&Secp256k1::signing_only()) | ||
| .x_only_public_key() | ||
| .0 | ||
| } | ||
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| #[test] | ||
| fn roundtrip_preserves_secret_variant() { | ||
| let (scan, spend) = test_keys(); | ||
| let original = SilentPaymentKeysFile::new(scan, SpendKey::Secret(spend)); | ||
| let bytes = original.to_bytes(); | ||
| let decoded = SilentPaymentKeysFile::from_bytes(&bytes).expect("decode"); | ||
| assert_eq!(original, decoded); | ||
| } | ||
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| #[test] | ||
| fn roundtrip_preserves_xonly_public_variant() { | ||
| let (scan, spend) = test_keys(); | ||
| let xonly = xonly_from(spend); | ||
| let original = SilentPaymentKeysFile::new(scan, SpendKey::XOnlyPublic(xonly)); | ||
| let bytes = original.to_bytes(); | ||
| let decoded = SilentPaymentKeysFile::from_bytes(&bytes).expect("decode"); | ||
| assert_eq!(original, decoded); | ||
| } | ||
|
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| #[test] | ||
| fn from_bytes_rejects_bad_magic() { | ||
| let (scan, spend) = test_keys(); | ||
| let mut bytes = b"XXXX".to_vec(); | ||
| bytes.extend_from_slice(&scan.secret_bytes()); | ||
| bytes.push(SPEND_TAG_SECRET); | ||
| bytes.extend_from_slice(&spend.secret_bytes()); | ||
| assert!(matches!( | ||
| SilentPaymentKeysFile::from_bytes(&bytes), | ||
| Err(KeysFileError::BadMagic) | ||
| )); | ||
| } | ||
|
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| #[test] | ||
| fn from_bytes_rejects_unknown_spend_tag() { | ||
| let (scan, spend) = test_keys(); | ||
| let mut bytes = MAGIC.to_vec(); | ||
| bytes.extend_from_slice(&scan.secret_bytes()); | ||
| bytes.push(99); | ||
| bytes.extend_from_slice(&spend.secret_bytes()); | ||
| assert!(matches!( | ||
| SilentPaymentKeysFile::from_bytes(&bytes), | ||
| Err(KeysFileError::UnknownSpendTag(99)) | ||
| )); | ||
| } | ||
|
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| #[test] | ||
| fn save_load_roundtrips_through_disk() { | ||
| let (scan, spend) = test_keys(); | ||
| let original = SilentPaymentKeysFile::new(scan, SpendKey::Secret(spend)); | ||
| let dir = tempfile::tempdir().expect("tempdir"); | ||
| let path = dir.path().join("keys.bin"); | ||
| original.save(&path).expect("save"); | ||
| let decoded = SilentPaymentKeysFile::load(&path).expect("load"); | ||
| assert_eq!(original, decoded); | ||
| } | ||
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| #[test] | ||
| fn save_refuses_to_overwrite_existing_file() { | ||
| let (scan, spend) = test_keys(); | ||
| let file = SilentPaymentKeysFile::new(scan, SpendKey::Secret(spend)); | ||
| let dir = tempfile::tempdir().expect("tempdir"); | ||
| let path = dir.path().join("keys.bin"); | ||
| file.save(&path).expect("first save"); | ||
| let err = file.save(&path).expect_err("second save must fail"); | ||
| assert!( | ||
| matches!(&err, KeysFileError::Io(e) if e.kind() == io::ErrorKind::AlreadyExists), | ||
| "expected Io(AlreadyExists), got {err:?}" | ||
| ); | ||
| } | ||
| } | ||
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