openssl/
derive.rs

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1//! Shared secret derivation.
2//!
3//! # Example
4//!
5//! The following example implements [ECDH] using `NIST P-384` keys:
6//!
7//! ```
8//! # fn main() -> Result<(), Box<dyn std::error::Error>> {
9//! # use std::convert::TryInto;
10//! use openssl::bn::BigNumContext;
11//! use openssl::pkey::PKey;
12//! use openssl::derive::Deriver;
13//! use openssl::ec::{EcGroup, EcKey, EcPoint, PointConversionForm};
14//! use openssl::nid::Nid;
15//!
16//! let group = EcGroup::from_curve_name(Nid::SECP384R1)?;
17//!
18//! let first: PKey<_> = EcKey::generate(&group)?.try_into()?;
19//!
20//! // second party generates an ephemeral key and derives
21//! // a shared secret using first party's public key
22//! let shared_key = EcKey::generate(&group)?;
23//! // shared_public is sent to first party
24//! let mut ctx = BigNumContext::new()?;
25//! let shared_public = shared_key.public_key().to_bytes(
26//!        &group,
27//!        PointConversionForm::COMPRESSED,
28//!        &mut ctx,
29//!    )?;
30//!
31//! let shared_key: PKey<_> = shared_key.try_into()?;
32//! let mut deriver = Deriver::new(&shared_key)?;
33//! deriver.set_peer(&first)?;
34//! // secret can be used e.g. as a symmetric encryption key
35//! let secret = deriver.derive_to_vec()?;
36//! # drop(deriver);
37//!
38//! // first party derives the same shared secret using
39//! // shared_public
40//! let point = EcPoint::from_bytes(&group, &shared_public, &mut ctx)?;
41//! let recipient_key: PKey<_> = EcKey::from_public_key(&group, &point)?.try_into()?;
42//! let mut deriver = Deriver::new(&first)?;
43//! deriver.set_peer(&recipient_key)?;
44//! let first_secret = deriver.derive_to_vec()?;
45//!
46//! assert_eq!(secret, first_secret);
47//! # Ok(()) }
48//! ```
49//!
50//! [ECDH]: https://wiki.openssl.org/index.php/Elliptic_Curve_Diffie_Hellman
51
52use foreign_types::ForeignTypeRef;
53use std::marker::PhantomData;
54use std::ptr;
55
56use crate::error::ErrorStack;
57use crate::pkey::{HasPrivate, HasPublic, PKeyRef};
58use crate::{cvt, cvt_p};
59use openssl_macros::corresponds;
60
61/// A type used to derive a shared secret between two keys.
62pub struct Deriver<'a>(*mut ffi::EVP_PKEY_CTX, PhantomData<&'a ()>);
63
64unsafe impl Sync for Deriver<'_> {}
65unsafe impl Send for Deriver<'_> {}
66
67#[allow(clippy::len_without_is_empty)]
68impl<'a> Deriver<'a> {
69    /// Creates a new `Deriver` using the provided private key.
70    ///
71    /// This corresponds to [`EVP_PKEY_derive_init`].
72    ///
73    /// [`EVP_PKEY_derive_init`]: https://www.openssl.org/docs/manmaster/crypto/EVP_PKEY_derive_init.html
74    pub fn new<T>(key: &'a PKeyRef<T>) -> Result<Deriver<'a>, ErrorStack>
75    where
76        T: HasPrivate,
77    {
78        unsafe {
79            cvt_p(ffi::EVP_PKEY_CTX_new(key.as_ptr(), ptr::null_mut()))
80                .map(|p| Deriver(p, PhantomData))
81                .and_then(|ctx| cvt(ffi::EVP_PKEY_derive_init(ctx.0)).map(|_| ctx))
82        }
83    }
84
85    /// Sets the peer key used for secret derivation.
86    #[corresponds(EVP_PKEY_derive_set_peer)]
87    pub fn set_peer<T>(&mut self, key: &'a PKeyRef<T>) -> Result<(), ErrorStack>
88    where
89        T: HasPublic,
90    {
91        unsafe { cvt(ffi::EVP_PKEY_derive_set_peer(self.0, key.as_ptr())).map(|_| ()) }
92    }
93
94    /// Sets the peer key used for secret derivation along with optionally validating the peer public key.
95    ///
96    /// Requires OpenSSL 3.0.0 or newer.
97    #[corresponds(EVP_PKEY_derive_set_peer_ex)]
98    #[cfg(ossl300)]
99    pub fn set_peer_ex<T>(
100        &mut self,
101        key: &'a PKeyRef<T>,
102        validate_peer: bool,
103    ) -> Result<(), ErrorStack>
104    where
105        T: HasPublic,
106    {
107        unsafe {
108            cvt(ffi::EVP_PKEY_derive_set_peer_ex(
109                self.0,
110                key.as_ptr(),
111                validate_peer as i32,
112            ))
113            .map(|_| ())
114        }
115    }
116
117    /// Returns the size of the shared secret.
118    ///
119    /// It can be used to size the buffer passed to [`Deriver::derive`].
120    ///
121    /// This corresponds to [`EVP_PKEY_derive`].
122    ///
123    /// [`Deriver::derive`]: #method.derive
124    /// [`EVP_PKEY_derive`]: https://www.openssl.org/docs/manmaster/crypto/EVP_PKEY_derive_init.html
125    pub fn len(&mut self) -> Result<usize, ErrorStack> {
126        unsafe {
127            let mut len = 0;
128            cvt(ffi::EVP_PKEY_derive(self.0, ptr::null_mut(), &mut len)).map(|_| len)
129        }
130    }
131
132    /// Derives a shared secret between the two keys, writing it into the buffer.
133    ///
134    /// Returns the number of bytes written.
135    ///
136    /// This corresponds to [`EVP_PKEY_derive`].
137    ///
138    /// [`EVP_PKEY_derive`]: https://www.openssl.org/docs/manmaster/crypto/EVP_PKEY_derive_init.html
139    pub fn derive(&mut self, buf: &mut [u8]) -> Result<usize, ErrorStack> {
140        let mut len = buf.len();
141        unsafe {
142            cvt(ffi::EVP_PKEY_derive(
143                self.0,
144                buf.as_mut_ptr() as *mut _,
145                &mut len,
146            ))
147            .map(|_| len)
148        }
149    }
150
151    /// A convenience function which derives a shared secret and returns it in a new buffer.
152    ///
153    /// This simply wraps [`Deriver::len`] and [`Deriver::derive`].
154    ///
155    /// [`Deriver::len`]: #method.len
156    /// [`Deriver::derive`]: #method.derive
157    pub fn derive_to_vec(&mut self) -> Result<Vec<u8>, ErrorStack> {
158        let len = self.len()?;
159        let mut buf = vec![0; len];
160        let len = self.derive(&mut buf)?;
161        buf.truncate(len);
162        Ok(buf)
163    }
164}
165
166impl Drop for Deriver<'_> {
167    fn drop(&mut self) {
168        unsafe {
169            ffi::EVP_PKEY_CTX_free(self.0);
170        }
171    }
172}
173
174#[cfg(test)]
175mod test {
176    use super::*;
177
178    use crate::ec::{EcGroup, EcKey};
179    use crate::nid::Nid;
180    use crate::pkey::PKey;
181
182    #[test]
183    fn derive_without_peer() {
184        let group = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1).unwrap();
185        let ec_key = EcKey::generate(&group).unwrap();
186        let pkey = PKey::from_ec_key(ec_key).unwrap();
187        let mut deriver = Deriver::new(&pkey).unwrap();
188        deriver.derive_to_vec().unwrap_err();
189    }
190
191    #[test]
192    fn test_ec_key_derive() {
193        let group = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1).unwrap();
194        let ec_key = EcKey::generate(&group).unwrap();
195        let ec_key2 = EcKey::generate(&group).unwrap();
196        let pkey = PKey::from_ec_key(ec_key).unwrap();
197        let pkey2 = PKey::from_ec_key(ec_key2).unwrap();
198        let mut deriver = Deriver::new(&pkey).unwrap();
199        deriver.set_peer(&pkey2).unwrap();
200        let shared = deriver.derive_to_vec().unwrap();
201        assert!(!shared.is_empty());
202    }
203
204    #[test]
205    #[cfg(ossl300)]
206    fn test_ec_key_derive_ex() {
207        let group = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1).unwrap();
208        let ec_key = EcKey::generate(&group).unwrap();
209        let ec_key2 = EcKey::generate(&group).unwrap();
210        let pkey = PKey::from_ec_key(ec_key).unwrap();
211        let pkey2 = PKey::from_ec_key(ec_key2).unwrap();
212        let mut deriver = Deriver::new(&pkey).unwrap();
213        deriver.set_peer_ex(&pkey2, true).unwrap();
214        let shared = deriver.derive_to_vec().unwrap();
215        assert!(!shared.is_empty());
216    }
217}
openssl/derive.rs

openssl/
derive.rs
