feat: traits: add traits for encryption and decryption

Add traits following the signature design for encryption and decryption.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

src/lib.rs

@@ -222,6 +222,7 @@ pub mod algorithms;
 pub mod errors;
 pub mod pkcs1v15;
 pub mod pss;
+pub mod traits;
 
 mod dummy_rng;
 mod encoding;

src/traits.rs

@@ -0,0 +1,42 @@
+//! Generic traits for message encryption and decryption
+
+use alloc::vec::Vec;
+use rand_core::CryptoRngCore;
+
+use crate::errors::Result;
+
+/// Encrypt the message using provided random source
+pub trait RandomizedEncryptor {
+    /// Encrypt the given message.
+    fn encrypt_with_rng<R: CryptoRngCore + ?Sized>(
+        &self,
+        rng: &mut R,
+        msg: &[u8],
+    ) -> Result<Vec<u8>>;
+}
+
+/// Decrypt the given message
+pub trait Decryptor {
+    /// Decrypt the given message.
+    fn decrypt(&self, ciphertext: &[u8]) -> Result<Vec<u8>>;
+}
+
+/// Decrypt the given message using provided random source
+pub trait RandomizedDecryptor {
+    /// Decrypt the given message.
+    fn decrypt_with_rng<R: CryptoRngCore + ?Sized>(
+        &self,
+        rng: &mut R,
+        ciphertext: &[u8],
+    ) -> Result<Vec<u8>>;
+}
+
+/// Encryption keypair with an associated encryption key.
+pub trait EncryptingKeypair {
+    /// Encrypting key type for this keypair.
+    type EncryptingKey: Clone;
+
+    /// Get the encrypting key which can encrypt messages to be decrypted by
+    /// the decryption key portion of this keypair.
+    fn encrypting_key(&self) -> Self::EncryptingKey;
+}