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rust-secp256k1-unsafe-fast
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Merge pull request #201 from elichai/2020-03-ecdh 

Simplify callback logic to returning raw coordinates
This commit is contained in:
Andrew Poelstra 2020-04-06 14:48:57 +00:00 committed by GitHub
parent 3fd089712c 2eff118d03
commit 86751b2d74
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3 changed files with 49 additions and 115 deletions
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4
no_std_test/src/main.rs
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@ -105,10 +105,10 @@ fn start(_argc: isize, _argv: *const *const u8) -> isize {
let _ = SharedSecret::new(&public_key, &secret_key); let _ = SharedSecret::new(&public_key, &secret_key);
let mut x_arr = [0u8; 32]; let mut x_arr = [0u8; 32];
let y_arr = unsafe { SharedSecret::new_with_hash_no_panic(&public_key, &secret_key, |x,y| { let y_arr = SharedSecret::new_with_hash(&public_key, &secret_key, |x,y| {
x_arr = x; x_arr = x;
y.into() y.into()
})}.unwrap(); });
assert_ne!(x_arr, [0u8; 32]); assert_ne!(x_arr, [0u8; 32]);
assert_ne!(&y_arr[..], &[0u8; 32][..]); assert_ne!(&y_arr[..], &[0u8; 32][..]);

157
src/ecdh.rs
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@ -22,7 +22,6 @@ use core::ops::{FnMut, Deref};
use key::{SecretKey, PublicKey}; use key::{SecretKey, PublicKey};
use ffi::{self, CPtr}; use ffi::{self, CPtr};
use secp256k1_sys::types::{c_int, c_uchar, c_void}; use secp256k1_sys::types::{c_int, c_uchar, c_void};
use Error;
/// A tag used for recovering the public key from a compact signature /// A tag used for recovering the public key from a compact signature
#[derive(Copy, Clone)] #[derive(Copy, Clone)]
@ -89,39 +88,12 @@ impl Deref for SharedSecret {
} }
unsafe fn callback_logic<F>(output: *mut c_uchar, x: *const c_uchar, y: *const c_uchar, data: *mut c_void) -> c_int unsafe extern "C" fn c_callback(output: *mut c_uchar, x: *const c_uchar, y: *const c_uchar, _data: *mut c_void) -> c_int {
where F: FnMut([u8; 32], [u8; 32]) -> SharedSecret { ptr::copy_nonoverlapping(x, output, 32);
let callback: &mut F = &mut *(data as *mut F); ptr::copy_nonoverlapping(y, output.offset(32), 32);
1
let mut x_arr = [0; 32];
let mut y_arr = [0; 32];
ptr::copy_nonoverlapping(x, x_arr.as_mut_ptr(), 32);
ptr::copy_nonoverlapping(y, y_arr.as_mut_ptr(), 32);
let secret = callback(x_arr, y_arr);
ptr::copy_nonoverlapping(secret.as_ptr(), output as *mut u8, secret.len());
secret.len() as c_int
} }
#[cfg(feature = "std")]
unsafe extern "C" fn hash_callback_catch_unwind<F>(output: *mut c_uchar, x: *const c_uchar, y: *const c_uchar, data: *mut c_void) -> c_int
where F: FnMut([u8; 32], [u8; 32]) -> SharedSecret {
let res = ::std::panic::catch_unwind(||callback_logic::<F>(output, x, y, data));
if let Ok(len) = res {
len
} else {
-1
}
}
unsafe extern "C" fn hash_callback_unsafe<F>(output: *mut c_uchar, x: *const c_uchar, y: *const c_uchar, data: *mut c_void) -> c_int
where F: FnMut([u8; 32], [u8; 32]) -> SharedSecret {
callback_logic::<F>(output, x, y, data)
}
impl SharedSecret { impl SharedSecret {
/// Creates a new shared secret from a pubkey and secret key /// Creates a new shared secret from a pubkey and secret key
#[inline] #[inline]
@ -137,35 +109,17 @@ impl SharedSecret {
ptr::null_mut(), ptr::null_mut(),
) )
}; };
debug_assert_eq!(res, 1); // The default `secp256k1_ecdh_hash_function_default` should always return 1. // The default `secp256k1_ecdh_hash_function_default` should always return 1.
// and the scalar was verified to be valid(0 > scalar > group_order) via the type system
debug_assert_eq!(res, 1);
ss.set_len(32); // The default hash function is SHA256, which is 32 bytes long. ss.set_len(32); // The default hash function is SHA256, which is 32 bytes long.
ss ss
} }
fn new_with_callback_internal<F>(point: &PublicKey, scalar: &SecretKey, mut closure: F, callback: ffi::EcdhHashFn) -> Result<SharedSecret, Error>
where F: FnMut([u8; 32], [u8; 32]) -> SharedSecret {
let mut ss = SharedSecret::empty();
let res = unsafe {
ffi::secp256k1_ecdh(
ffi::secp256k1_context_no_precomp,
ss.get_data_mut_ptr(),
point.as_ptr(),
scalar.as_ptr(),
callback,
&mut closure as *mut F as *mut c_void,
)
};
if res == -1 {
return Err(Error::CallbackPanicked);
}
debug_assert!(res >= 16); // 128 bit is the minimum for a secure hash function and the minimum we let users.
ss.set_len(res as usize);
Ok(ss)
}
/// Creates a new shared secret from a pubkey and secret key with applied custom hash function /// Creates a new shared secret from a pubkey and secret key with applied custom hash function
/// The custom hash function must be in the form of `fn(x: [u8;32], y: [u8;32]) -> SharedSecret`
/// `SharedSecret` can be easily created via the `From` impl from arrays.
/// # Examples /// # Examples
/// ``` /// ```
/// # use secp256k1::ecdh::SharedSecret; /// # use secp256k1::ecdh::SharedSecret;
@ -182,43 +136,29 @@ impl SharedSecret {
/// }); /// });
/// ///
/// ``` /// ```
#[cfg(feature = "std")] pub fn new_with_hash<F>(point: &PublicKey, scalar: &SecretKey, mut hash_function: F) -> SharedSecret
pub fn new_with_hash<F>(point: &PublicKey, scalar: &SecretKey, hash_function: F) -> Result<SharedSecret, Error>
where F: FnMut([u8; 32], [u8; 32]) -> SharedSecret { where F: FnMut([u8; 32], [u8; 32]) -> SharedSecret {
Self::new_with_callback_internal(point, scalar, hash_function, hash_callback_catch_unwind::<F>) let mut xy = [0u8; 64];
}
/// Creates a new shared secret from a pubkey and secret key with applied custom hash function let res = unsafe {
/// Note that this function is the same as [`new_with_hash`] ffi::secp256k1_ecdh(
/// ffi::secp256k1_context_no_precomp,
/// # Safety xy.as_mut_ptr(),
/// The function doesn't wrap the callback with [`catch_unwind`] point.as_ptr(),
/// so if the callback panics it will panic through an FFI boundray which is [`Undefined Behavior`] scalar.as_ptr(),
/// If possible you should use [`new_with_hash`] which does wrap the callback with [`catch_unwind`] so is safe to use. c_callback,
/// ptr::null_mut(),
/// [`catch_unwind`]: https://doc.rust-lang.org/std/panic/fn.catch_unwind.html )
/// [`Undefined Behavior`]: https://doc.rust-lang.org/nomicon/ffi.html#ffi-and-panics };
/// [`new_with_hash`]: #method.new_with_hash // Our callback *always* returns 1.
/// # Examples // and the scalar was verified to be valid(0 > scalar > group_order) via the type system
/// ``` debug_assert_eq!(res, 1);
/// # use secp256k1::ecdh::SharedSecret;
/// # use secp256k1::{Secp256k1, PublicKey, SecretKey}; let mut x = [0u8; 32];
/// # fn sha2(_a: &[u8], _b: &[u8]) -> [u8; 32] {[0u8; 32]} let mut y = [0u8; 32];
/// # let secp = Secp256k1::signing_only(); x.copy_from_slice(&xy[..32]);
/// # let secret_key = SecretKey::from_slice(&[3u8; 32]).unwrap(); y.copy_from_slice(&xy[32..]);
/// # let secret_key2 = SecretKey::from_slice(&[7u8; 32]).unwrap(); hash_function(x, y)
/// # let public_key = PublicKey::from_secret_key(&secp, &secret_key2);
//
/// let secret = unsafe { SharedSecret::new_with_hash_no_panic(&public_key, &secret_key, |x,y| {
/// let hash: [u8; 32] = sha2(&x,&y);
/// hash.into()
/// })};
///
///
/// ```
pub unsafe fn new_with_hash_no_panic<F>(point: &PublicKey, scalar: &SecretKey, hash_function: F) -> Result<SharedSecret, Error>
where F: FnMut([u8; 32], [u8; 32]) -> SharedSecret {
Self::new_with_callback_internal(point, scalar, hash_function, hash_callback_unsafe::<F>)
} }
} }
@ -248,9 +188,9 @@ mod tests {
let (sk1, pk1) = s.generate_keypair(&mut thread_rng()); let (sk1, pk1) = s.generate_keypair(&mut thread_rng());
let (sk2, pk2) = s.generate_keypair(&mut thread_rng()); let (sk2, pk2) = s.generate_keypair(&mut thread_rng());
let sec1 = SharedSecret::new_with_hash(&pk1, &sk2, |x,_| x.into()).unwrap(); let sec1 = SharedSecret::new_with_hash(&pk1, &sk2, |x,_| x.into());
let sec2 = SharedSecret::new_with_hash(&pk2, &sk1, |x,_| x.into()).unwrap(); let sec2 = SharedSecret::new_with_hash(&pk2, &sk1, |x,_| x.into());
let sec_odd = SharedSecret::new_with_hash(&pk1, &sk1, |x,_| x.into()).unwrap(); let sec_odd = SharedSecret::new_with_hash(&pk1, &sk1, |x,_| x.into());
assert_eq!(sec1, sec2); assert_eq!(sec1, sec2);
assert_ne!(sec_odd, sec2); assert_ne!(sec_odd, sec2);
} }
@ -262,32 +202,29 @@ mod tests {
let expect_result: [u8; 64] = [123; 64]; let expect_result: [u8; 64] = [123; 64];
let mut x_out = [0u8; 32]; let mut x_out = [0u8; 32];
let mut y_out = [0u8; 32]; let mut y_out = [0u8; 32];
let result = SharedSecret::new_with_hash(&pk1, &sk1, | x, y | { let result = SharedSecret::new_with_hash(&pk1, &sk1, |x, y| {
x_out = x; x_out = x;
y_out = y; y_out = y;
expect_result.into() expect_result.into()
}).unwrap(); });
let result_unsafe = unsafe {SharedSecret::new_with_hash_no_panic(&pk1, &sk1, | x, y | {
x_out = x;
y_out = y;
expect_result.into()
}).unwrap()};
assert_eq!(&expect_result[..], &result[..]); assert_eq!(&expect_result[..], &result[..]);
assert_eq!(result, result_unsafe);
assert_ne!(x_out, [0u8; 32]); assert_ne!(x_out, [0u8; 32]);
assert_ne!(y_out, [0u8; 32]); assert_ne!(y_out, [0u8; 32]);
} }
#[test] #[test]
fn ecdh_with_hash_callback_panic() { fn test_c_callback() {
let s = Secp256k1::signing_only(); let x = [5u8; 32];
let (sk1, pk1) = s.generate_keypair(&mut thread_rng()); let y = [7u8; 32];
let mut res = [0u8; 48]; let mut output = [0u8; 64];
let result = SharedSecret::new_with_hash(&pk1, &sk1, | x, _ | { let res = unsafe { super::c_callback(output.as_mut_ptr(), x.as_ptr(), y.as_ptr(), ::ptr::null_mut()) };
res.copy_from_slice(&x); // res.len() != x.len(). this will panic. assert_eq!(res, 1);
res.into() let mut new_x = [0u8; 32];
}); let mut new_y = [0u8; 32];
assert_eq!(result, Err(Error::CallbackPanicked)); new_x.copy_from_slice(&output[..32]);
new_y.copy_from_slice(&output[32..]);
assert_eq!(x, new_x);
assert_eq!(y, new_y);
} }
} }

3
src/lib.rs
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@ -496,8 +496,6 @@ pub enum Error {
InvalidTweak, InvalidTweak,
/// Didn't pass enough memory to context creation with preallocated memory /// Didn't pass enough memory to context creation with preallocated memory
NotEnoughMemory, NotEnoughMemory,
/// The callback has panicked.
CallbackPanicked,
} }
impl Error { impl Error {
@ -511,7 +509,6 @@ impl Error {
Error::InvalidRecoveryId => "secp: bad recovery id", Error::InvalidRecoveryId => "secp: bad recovery id",
Error::InvalidTweak => "secp: bad tweak", Error::InvalidTweak => "secp: bad tweak",
Error::NotEnoughMemory => "secp: not enough memory allocated", Error::NotEnoughMemory => "secp: not enough memory allocated",
Error::CallbackPanicked => "secp: a callback passed has panicked",
} }
} }
} }