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//! Shared secret derivation.
use foreign_types::ForeignTypeRef;
use std::marker::PhantomData;
use std::ptr;
use crate::error::ErrorStack;
use crate::pkey::{HasPrivate, HasPublic, PKeyRef};
use crate::{cvt, cvt_p};
/// A type used to derive a shared secret between two keys.
pub struct Deriver<'a>(*mut ffi::EVP_PKEY_CTX, PhantomData<&'a ()>);
unsafe impl<'a> Sync for Deriver<'a> {}
unsafe impl<'a> Send for Deriver<'a> {}
#[allow(clippy::len_without_is_empty)]
impl<'a> Deriver<'a> {
/// Creates a new `Deriver` using the provided private key.
///
/// This corresponds to [`EVP_PKEY_derive_init`].
///
/// [`EVP_PKEY_derive_init`]: https://www.openssl.org/docs/man1.0.2/crypto/EVP_PKEY_derive_init.html
pub fn new<T>(key: &'a PKeyRef<T>) -> Result<Deriver<'a>, ErrorStack>
where
T: HasPrivate,
{
unsafe {
cvt_p(ffi::EVP_PKEY_CTX_new(key.as_ptr(), ptr::null_mut()))
.map(|p| Deriver(p, PhantomData))
.and_then(|ctx| cvt(ffi::EVP_PKEY_derive_init(ctx.0)).map(|_| ctx))
}
}
/// Sets the peer key used for secret derivation.
///
/// This corresponds to [`EVP_PKEY_derive_set_peer`]:
///
/// [`EVP_PKEY_derive_set_peer`]: https://www.openssl.org/docs/man1.0.2/crypto/EVP_PKEY_derive_init.html
pub fn set_peer<T>(&mut self, key: &'a PKeyRef<T>) -> Result<(), ErrorStack>
where
T: HasPublic,
{
unsafe { cvt(ffi::EVP_PKEY_derive_set_peer(self.0, key.as_ptr())).map(|_| ()) }
}
/// Returns the size of the shared secret.
///
/// It can be used to size the buffer passed to [`Deriver::derive`].
///
/// This corresponds to [`EVP_PKEY_derive`].
///
/// [`Deriver::derive`]: #method.derive
/// [`EVP_PKEY_derive`]: https://www.openssl.org/docs/man1.0.2/crypto/EVP_PKEY_derive_init.html
pub fn len(&mut self) -> Result<usize, ErrorStack> {
unsafe {
let mut len = 0;
cvt(ffi::EVP_PKEY_derive(self.0, ptr::null_mut(), &mut len)).map(|_| len)
}
}
/// Derives a shared secret between the two keys, writing it into the buffer.
///
/// Returns the number of bytes written.
///
/// This corresponds to [`EVP_PKEY_derive`].
///
/// [`EVP_PKEY_derive`]: https://www.openssl.org/docs/man1.0.2/crypto/EVP_PKEY_derive_init.html
pub fn derive(&mut self, buf: &mut [u8]) -> Result<usize, ErrorStack> {
let mut len = buf.len();
unsafe {
cvt(ffi::EVP_PKEY_derive(
self.0,
buf.as_mut_ptr() as *mut _,
&mut len,
))
.map(|_| len)
}
}
/// A convenience function which derives a shared secret and returns it in a new buffer.
///
/// This simply wraps [`Deriver::len`] and [`Deriver::derive`].
///
/// [`Deriver::len`]: #method.len
/// [`Deriver::derive`]: #method.derive
pub fn derive_to_vec(&mut self) -> Result<Vec<u8>, ErrorStack> {
let len = self.len()?;
let mut buf = vec![0; len];
let len = self.derive(&mut buf)?;
buf.truncate(len);
Ok(buf)
}
}
#[cfg(test)]
mod test {
use super::*;
use crate::ec::{EcGroup, EcKey};
use crate::nid::Nid;
use crate::pkey::PKey;
#[test]
fn derive_without_peer() {
let group = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1).unwrap();
let ec_key = EcKey::generate(&group).unwrap();
let pkey = PKey::from_ec_key(ec_key).unwrap();
let mut deriver = Deriver::new(&pkey).unwrap();
deriver.derive_to_vec().unwrap_err();
}
#[test]
fn test_ec_key_derive() {
let group = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1).unwrap();
let ec_key = EcKey::generate(&group).unwrap();
let ec_key2 = EcKey::generate(&group).unwrap();
let pkey = PKey::from_ec_key(ec_key).unwrap();
let pkey2 = PKey::from_ec_key(ec_key2).unwrap();
let mut deriver = Deriver::new(&pkey).unwrap();
deriver.set_peer(&pkey2).unwrap();
let shared = deriver.derive_to_vec().unwrap();
assert!(!shared.is_empty());
}
}
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