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}
218