openpgp: Add a type that combines S2K, cipher, and session key.

  - I'm happy to wordsmith the name, EncryptionParameters isn't
    quite ideal...

2 files changed, 46 insertions, 1 deletions

diff --git a/openpgp/src/crypto/mod.rs b/openpgp/src/crypto/mod.rs
index 1c136102..633bb2b2 100644
--- a/openpgp/src/crypto/mod.rs
+++ b/openpgp/src/crypto/mod.rs
@@ -37,7 +37,7 @@ pub mod hash;
 pub mod mem;
 pub mod mpi;
 mod s2k;
-pub use s2k::S2K;
+pub use s2k::{EncryptionParameters, S2K};
 pub(crate) mod symmetric;
 
 #[cfg(test)]
diff --git a/openpgp/src/crypto/s2k.rs b/openpgp/src/crypto/s2k.rs
index 9b7c24d6..d61f7969 100644
--- a/openpgp/src/crypto/s2k.rs
+++ b/openpgp/src/crypto/s2k.rs
@@ -9,6 +9,7 @@
 use crate::Error;
 use crate::Result;
 use crate::HashAlgorithm;
+use crate::types::SymmetricAlgorithm;
 use crate::crypto::Password;
 use crate::crypto::SessionKey;
 use crate::crypto::hash::Digest;
@@ -162,6 +163,24 @@ impl S2K {
         }
     }
 
+    /// Makes encryption parameters.
+    ///
+    /// An `EncryptionParameters` object can be used to encrypt and
+    /// decrypt secret key material.
+    pub fn make_encryption_parameters<A>(&self, password: &Password, algo: A)
+                                         -> Result<EncryptionParameters>
+    where
+        A: Into<Option<SymmetricAlgorithm>>,
+    {
+        let algo = algo.into().unwrap_or_default();
+        let key = self.derive_key(password, algo.key_size()?)?;
+        Ok(EncryptionParameters {
+            algo,
+            key,
+            s2k: self.clone(),
+        })
+    }
+
     /// Derives a key of the given size from a password.
     pub fn derive_key(&self, password: &Password, key_size: usize)
     -> Result<SessionKey> {
@@ -415,6 +434,32 @@ impl Arbitrary for S2K {
     }
 }
 
+/// XXX
+pub struct EncryptionParameters {
+    algo: SymmetricAlgorithm,
+    s2k: S2K,
+    key: SessionKey,
+}
+
+impl EncryptionParameters {
+    /// Returns the symmetric algorithm.
+    pub fn algo(&self) -> SymmetricAlgorithm {
+        self.algo
+    }
+
+    /// Returns the S2K parameters.
+    pub fn s2k(&self) -> &S2K {
+        &self.s2k
+    }
+
+    /// Returns the symmetric key derived from the S2K object and the
+    /// password.
+    pub fn key(&self) -> &SessionKey {
+        &self.key
+    }
+
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;