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Merge pull request #180 from elichai/2019-11-SharedSecret 

Alternative: Passing custom hash functions to ECDH
This commit is contained in:
Andrew Poelstra 2019-12-09 21:11:30 +00:00 committed by GitHub
parent e7f0974f08 92c42ca9e6
commit 4b740911c6
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
6 changed files with 273 additions and 86 deletions
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11
no_std_test/src/main.rs
View File

@ -55,6 +55,7 @@ use core::panic::PanicInfo;
use secp256k1::rand::{self, RngCore};
use secp256k1::serde::Serialize;
use secp256k1::*;
use secp256k1::ecdh::SharedSecret;
use serde_cbor::de;
use serde_cbor::ser::SliceWrite;
@ -102,6 +103,16 @@ fn start(_argc: isize, _argv: *const *const u8) -> isize {
let new_sig: Signature = de::from_mut_slice(&mut cbor_ser[..size]).unwrap();
assert_eq!(sig, new_sig);
let _ = SharedSecret::new(&public_key, &secret_key);
let mut x_arr = [0u8; 32];
let y_arr = unsafe { SharedSecret::new_with_hash_no_panic(&public_key, &secret_key, |x,y| {
x_arr = x;
y.into()
})}.unwrap();
assert_ne!(x_arr, [0u8; 32]);
assert_ne!(&y_arr[..], &[0u8; 32][..]);
unsafe { libc::printf("Verified Successfully!\n\0".as_ptr() as _) };
0
}

37
secp256k1-sys/src/lib.rs
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@ -72,7 +72,7 @@ pub type EcdhHashFn = unsafe extern "C" fn(
x: *const c_uchar,
y: *const c_uchar,
data: *mut c_void,
);
) -> c_int;
/// A Secp256k1 context, containing various precomputed values and such
/// needed to do elliptic curve computations. If you create one of these
@ -134,25 +134,6 @@ impl Default for Signature {
}
}
/// Library-internal representation of an ECDH shared secret
#[repr(C)]
pub struct SharedSecret([c_uchar; 32]);
impl_array_newtype!(SharedSecret, c_uchar, 32);
impl_raw_debug!(SharedSecret);
impl SharedSecret {
/// Create a new (zeroed) signature usable for the FFI interface
pub fn new() -> SharedSecret { SharedSecret([0; 32]) }
/// Create a new (uninitialized) signature usable for the FFI interface
#[deprecated(since = "0.15.3", note = "Please use the new function instead")]
pub unsafe fn blank() -> SharedSecret { SharedSecret::new() }
}
impl Default for SharedSecret {
fn default() -> Self {
SharedSecret::new()
}
}
#[cfg(not(feature = "fuzztarget"))]
extern "C" {
@ -296,7 +277,7 @@ extern "C" {
#[cfg_attr(not(feature = "external-symbols"), link_name = "rustsecp256k1_v0_1_0_ecdh")]
pub fn secp256k1_ecdh(
cx: *const Context,
output: *mut SharedSecret,
output: *mut c_uchar,
pubkey: *const PublicKey,
privkey: *const c_uchar,
hashfp: EcdhHashFn,
@ -459,7 +440,7 @@ mod fuzz_dummy {
use self::std::{ptr, mem};
use self::std::boxed::Box;
use types::*;
use ::{Signature, Context, NonceFn, EcdhHashFn, PublicKey, SharedSecret,
use ::{Signature, Context, NonceFn, EcdhHashFn, PublicKey,
SECP256K1_START_NONE, SECP256K1_START_VERIFY, SECP256K1_START_SIGN,
SECP256K1_SER_COMPRESSED, SECP256K1_SER_UNCOMPRESSED};
@ -788,7 +769,7 @@ mod fuzz_dummy {
/// Sets out to point[0..16]||scalar[0..16]
pub unsafe fn secp256k1_ecdh(
cx: *const Context,
out: *mut SharedSecret,
out: *mut c_uchar,
point: *const PublicKey,
scalar: *const c_uchar,
_hashfp: EcdhHashFn,
@ -801,13 +782,13 @@ mod fuzz_dummy {
ptr::copy(scalar, scalar_prefix[..].as_mut_ptr(), 16);
if (*point).0[0..16] > scalar_prefix[0..16] {
(*out).0[0..16].copy_from_slice(&(*point).0[0..16]);
ptr::copy(scalar, (*out).0[16..32].as_mut_ptr(), 16);
ptr::copy((*point).as_ptr(), out, 16);
ptr::copy(scalar, out.offset(16), 16);
} else {
ptr::copy(scalar, (*out).0[0..16].as_mut_ptr(), 16);
(*out).0[16..32].copy_from_slice(&(*point).0[0..16]);
ptr::copy(scalar, out, 16);
ptr::copy((*point).as_ptr(), out.offset(16), 16);
}
(*out).0[16] = 0x00; // result should always be a valid secret key
(*out.offset(16)) = 0x00; // result should always be a valid secret key
1
}
}

1
secp256k1-sys/src/macros.rs
View File

@ -144,6 +144,7 @@ macro_rules! impl_array_newtype {
}
}
#[macro_export]
macro_rules! impl_raw_debug {
($thing:ident) => {
impl ::core::fmt::Debug for $thing {

289
src/ecdh.rs
View File

@ -16,83 +16,209 @@
//! Support for shared secret computations
//!
use core::{ops, ptr};
use core::ptr;
use core::ops::{FnMut, Deref};
use key::{SecretKey, PublicKey};
use ffi::{self, CPtr};
use secp256k1_sys::types::{c_int, c_uchar, c_void};
use Error;
/// A tag used for recovering the public key from a compact signature
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub struct SharedSecret(ffi::SharedSecret);
#[derive(Copy, Clone)]
pub struct SharedSecret {
data: [u8; 256],
len: usize,
}
impl_raw_debug!(SharedSecret);
// This implementes `From<N>` for all `[u8; N]` arrays from 128bits(16 byte) to 2048bits allowing known hash lengths.
// Lower than 128 bits isn't resistant to collisions any more.
impl_from_array_len!(SharedSecret, 256, (16 20 28 32 48 64 96 128 256));
impl SharedSecret {
/// Create an empty SharedSecret
pub(crate) fn empty() -> SharedSecret {
SharedSecret {
data: [0u8; 256],
len: 0,
}
}
/// Get a pointer to the underlying data with the specified capacity.
pub(crate) fn get_data_mut_ptr(&mut self) -> *mut u8 {
self.data.as_mut_ptr()
}
/// Get the capacity of the underlying data buffer.
pub fn capacity(&self) -> usize {
self.data.len()
}
/// Get the len of the used data.
pub fn len(&self) -> usize {
self.len
}
/// Set the length of the object.
pub(crate) fn set_len(&mut self, len: usize) {
debug_assert!(len <= self.data.len());
self.len = len;
}
}
impl PartialEq for SharedSecret {
fn eq(&self, other: &SharedSecret) -> bool {
self.as_ref() == other.as_ref()
}
}
impl AsRef<[u8]> for SharedSecret {
fn as_ref(&self) -> &[u8] {
&self.data[..self.len]
}
}
impl Deref for SharedSecret {
type Target = [u8];
fn deref(&self) -> &[u8] {
&self.data[..self.len]
}
}
unsafe fn callback_logic<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 callback: &mut F = &mut *(data as *mut F);
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 {
/// Creates a new shared secret from a pubkey and secret key
#[inline]
pub fn new(point: &PublicKey, scalar: &SecretKey) -> SharedSecret {
unsafe {
let mut ss = ffi::SharedSecret::new();
let res = ffi::secp256k1_ecdh(
let mut ss = SharedSecret::empty();
let res = unsafe {
ffi::secp256k1_ecdh(
ffi::secp256k1_context_no_precomp,
&mut ss,
ss.get_data_mut_ptr(),
point.as_c_ptr(),
scalar.as_c_ptr(),
ffi::secp256k1_ecdh_hash_function_default,
ptr::null_mut(),
);
debug_assert_eq!(res, 1);
SharedSecret(ss)
)
};
debug_assert_eq!(res, 1); // The default `secp256k1_ecdh_hash_function_default` should always return 1.
ss.set_len(32); // The default hash function is SHA256, which is 32 bytes long.
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)
}
/// Obtains a raw pointer suitable for use with FFI functions
#[inline]
pub fn as_ptr(&self) -> *const ffi::SharedSecret {
&self.0 as *const _
/// Creates a new shared secret from a pubkey and secret key with applied custom hash function
/// # Examples
/// ```
/// # use secp256k1::ecdh::SharedSecret;
/// # use secp256k1::{Secp256k1, PublicKey, SecretKey};
/// # fn sha2(_a: &[u8], _b: &[u8]) -> [u8; 32] {[0u8; 32]}
/// # let secp = Secp256k1::signing_only();
/// # let secret_key = SecretKey::from_slice(&[3u8; 32]).unwrap();
/// # let secret_key2 = SecretKey::from_slice(&[7u8; 32]).unwrap();
/// # let public_key = PublicKey::from_secret_key(&secp, &secret_key2);
///
/// let secret = SharedSecret::new_with_hash(&public_key, &secret_key, |x,y| {
/// let hash: [u8; 32] = sha2(&x,&y);
/// hash.into()
/// });
///
/// ```
#[cfg(feature = "std")]
pub fn new_with_hash<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_catch_unwind::<F>)
}
}
/// Creates a new shared secret from a FFI shared secret
impl From<ffi::SharedSecret> for SharedSecret {
#[inline]
fn from(ss: ffi::SharedSecret) -> SharedSecret {
SharedSecret(ss)
}
}
impl ops::Index<usize> for SharedSecret {
type Output = u8;
#[inline]
fn index(&self, index: usize) -> &u8 {
&self.0[index]
}
}
impl ops::Index<ops::Range<usize>> for SharedSecret {
type Output = [u8];
#[inline]
fn index(&self, index: ops::Range<usize>) -> &[u8] {
&self.0[index]
}
}
impl ops::Index<ops::RangeFrom<usize>> for SharedSecret {
type Output = [u8];
#[inline]
fn index(&self, index: ops::RangeFrom<usize>) -> &[u8] {
&self.0[index.start..]
}
}
impl ops::Index<ops::RangeFull> for SharedSecret {
type Output = [u8];
#[inline]
fn index(&self, _: ops::RangeFull) -> &[u8] {
&self.0[..]
/// Creates a new shared secret from a pubkey and secret key with applied custom hash function
/// Note that this function is the same as [`new_with_hash`]
///
/// # Safety
/// The function doesn't wrap the callback with [`catch_unwind`]
/// so if the callback panics it will panic through an FFI boundray which is [`Undefined Behavior`]
/// If possible you should use [`new_with_hash`] which does wrap the callback with [`catch_unwind`] so is safe to use.
///
/// [`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
/// # Examples
/// ```
/// # use secp256k1::ecdh::SharedSecret;
/// # use secp256k1::{Secp256k1, PublicKey, SecretKey};
/// # fn sha2(_a: &[u8], _b: &[u8]) -> [u8; 32] {[0u8; 32]}
/// # let secp = Secp256k1::signing_only();
/// # let secret_key = SecretKey::from_slice(&[3u8; 32]).unwrap();
/// # let secret_key2 = SecretKey::from_slice(&[7u8; 32]).unwrap();
/// # 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>)
}
}
@ -101,6 +227,7 @@ mod tests {
use rand::thread_rng;
use super::SharedSecret;
use super::super::Secp256k1;
use Error;
#[test]
fn ecdh() {
@ -114,6 +241,54 @@ mod tests {
assert_eq!(sec1, sec2);
assert!(sec_odd != sec2);
}
#[test]
fn ecdh_with_hash() {
let s = Secp256k1::signing_only();
let (sk1, pk1) = 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 sec2 = SharedSecret::new_with_hash(&pk2, &sk1, |x,_| x.into()).unwrap();
let sec_odd = SharedSecret::new_with_hash(&pk1, &sk1, |x,_| x.into()).unwrap();
assert_eq!(sec1, sec2);
assert_ne!(sec_odd, sec2);
}
#[test]
fn ecdh_with_hash_callback() {
let s = Secp256k1::signing_only();
let (sk1, pk1) = s.generate_keypair(&mut thread_rng());
let expect_result: [u8; 64] = [123; 64];
let mut x_out = [0u8; 32];
let mut y_out = [0u8; 32];
let result = SharedSecret::new_with_hash(&pk1, &sk1, | x, y | {
x_out = x;
y_out = y;
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!(result, result_unsafe);
assert_ne!(x_out, [0u8; 32]);
assert_ne!(y_out, [0u8; 32]);
}
#[test]
fn ecdh_with_hash_callback_panic() {
let s = Secp256k1::signing_only();
let (sk1, pk1) = s.generate_keypair(&mut thread_rng());
let mut res = [0u8; 48];
let result = SharedSecret::new_with_hash(&pk1, &sk1, | x, _ | {
res.copy_from_slice(&x); // res.len() != x.len(). this will panic.
res.into()
});
assert_eq!(result, Err(Error::CallbackPanicked));
}
}
#[cfg(all(test, feature = "unstable"))]

4
src/lib.rs
View File

@ -496,7 +496,8 @@ pub enum Error {
InvalidTweak,
/// Didn't pass enough memory to context creation with preallocated memory
NotEnoughMemory,
/// The callback has panicked.
CallbackPanicked,
}
impl Error {
@ -510,6 +511,7 @@ impl Error {
Error::InvalidRecoveryId => "secp: bad recovery id",
Error::InvalidTweak => "secp: bad tweak",
Error::NotEnoughMemory => "secp: not enough memory allocated",
Error::CallbackPanicked => "secp: a callback passed has panicked",
}
}
}

17
src/macros.rs
View File

@ -27,6 +27,23 @@ macro_rules! impl_pretty_debug {
}
}
macro_rules! impl_from_array_len {
($thing:ident, $capacity:tt, ($($N:tt)+)) => {
$(
impl From<[u8; $N]> for $thing {
fn from(arr: [u8; $N]) -> Self {
let mut data = [0u8; $capacity];
data[..$N].copy_from_slice(&arr);
$thing {
data,
len: $N,
}
}
}
)+
}
}
#[cfg(feature="serde")]
/// Implements `Serialize` and `Deserialize` for a type `$t` which represents
/// a newtype over a byte-slice over length `$len`. Type `$t` must implement