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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 
52 use foreign_types::ForeignTypeRef;
53 use std::marker::PhantomData;
54 use std::ptr;
55 
56 use crate::error::ErrorStack;
57 use crate::pkey::{HasPrivate, HasPublic, PKeyRef};
58 use crate::{cvt, cvt_p};
59 use openssl_macros::corresponds;
60 
61 /// A type used to derive a shared secret between two keys.
62 pub struct Deriver<'a>(*mut ffi::EVP_PKEY_CTX, PhantomData<&'a ()>);
63 
64 unsafe impl<'a> Sync for Deriver<'a> {}
65 unsafe impl<'a> Send for Deriver<'a> {}
66 
67 #[allow(clippy::len_without_is_empty)]
68 impl<'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
new<T>(key: &'a PKeyRef<T>) -> Result<Deriver<'a>, ErrorStack> where T: HasPrivate,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)]
set_peer<T>(&mut self, key: &'a PKeyRef<T>) -> Result<(), ErrorStack> where T: HasPublic,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)]
set_peer_ex<T>( &mut self, key: &'a PKeyRef<T>, validate_peer: bool, ) -> Result<(), ErrorStack> where T: HasPublic,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
len(&mut self) -> Result<usize, ErrorStack>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
derive(&mut self, buf: &mut [u8]) -> Result<usize, ErrorStack>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
derive_to_vec(&mut self) -> Result<Vec<u8>, ErrorStack>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 
166 impl<'a> Drop for Deriver<'a> {
drop(&mut self)167     fn drop(&mut self) {
168         unsafe {
169             ffi::EVP_PKEY_CTX_free(self.0);
170         }
171     }
172 }
173 
174 #[cfg(test)]
175 mod test {
176     use super::*;
177 
178     use crate::ec::{EcGroup, EcKey};
179     use crate::nid::Nid;
180     use crate::pkey::PKey;
181 
182     #[test]
derive_without_peer()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]
test_ec_key_derive()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)]
test_ec_key_derive_ex()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