Encryption! With test cases.

src/rsa/public.rs

@@ -1,5 +1,9 @@
 use cryptonum::{BarrettUCN,UCN};
-use rsa::core::{ACCEPTABLE_KEY_SIZES,pkcs1_pad,vp1};
+use digest::{FixedOutput,Input};
+use rand::{OsRng,Rng};
+use rsa::core::{ACCEPTABLE_KEY_SIZES,ep,pkcs1_pad,vp1,xor_vecs};
+use rsa::errors::RSAError;
+use rsa::oaep::OAEPParams;
 use rsa::signing_hashes::SigningHash;
 
 #[derive(Clone,Debug,PartialEq,Eq)]
@@ -39,4 +43,82 @@ impl RSAPublic {
         let em_  = pkcs1_pad(&shash.ident, &hash, self.byte_len);
         (em == em_)
     }
+
+    /// Encrypt the given data with the public key and parameters, returning
+    /// the encrypted blob or an error encountered during encryption.
+    ///
+    /// OAEP encoding is used for this process, which requires a random number
+    /// generator. This version of the function uses `OsRng`. If you want to
+    /// use your own RNG, use `encrypt_w_rng`.
+    pub fn encrypt<H:Clone + Input + FixedOutput>(&self, oaep: &OAEPParams<H>, msg: &[u8])
+        -> Result<Vec<u8>,RSAError>
+    {
+        let mut g = OsRng::new()?;
+        self.encrypt_with_rng(&mut g, oaep, msg)
+    }
+
+    /// Encrypt the given data with the public key and parameters, returning
+    /// the encrypted blob or an error encountered during encryption. This
+    /// version also allows you to provide your own RNG, if you really feel
+    /// like shooting yourself in the foot.
+    pub fn encrypt_with_rng<G,H>(&self, g: &mut G, oaep: &OAEPParams<H>, msg: &[u8])
+        -> Result<Vec<u8>,RSAError>
+      where G: Rng, H: Clone + Input + FixedOutput
+    {
+        if self.byte_len <= ((2 * oaep.hash_len()) + 2) {
+            return Err(RSAError::KeyTooSmallForHash);
+        }
+
+        let mut res = Vec::new();
+
+        for chunk in msg.chunks(self.byte_len - (2 * oaep.hash_len()) - 2) {
+            let mut newchunk = self.oaep_encrypt(g, oaep, chunk)?;
+            res.append(&mut newchunk)
+        }
+
+        Ok(res)
+    }
+
+    fn oaep_encrypt<G: Rng,H:Clone + Input + FixedOutput>(&self, g: &mut G, oaep: &OAEPParams<H>, msg: &[u8])
+        -> Result<Vec<u8>,RSAError>
+    {
+        // Step 1b
+        if msg.len() > (self.byte_len - (2 * oaep.hash_len()) - 2) {
+            return Err(RSAError::BadMessageSize)
+        }
+        // Step 2a
+        let mut lhash = oaep.hash(oaep.label.as_bytes());
+        // Step 2b
+        let num0s = self.byte_len - msg.len() - (2 * oaep.hash_len()) - 2;
+        let mut ps = Vec::new();
+        ps.resize(num0s, 0);
+        // Step 2c
+        let mut db = Vec::new();
+        db.append(&mut lhash);
+        db.append(&mut ps);
+        db.push(1);
+        db.extend_from_slice(msg);
+        // Step 2d
+        let seed : Vec<u8> = g.gen_iter().take(oaep.hash_len()).collect();
+        // Step 2e
+        let db_mask = oaep.mgf1(&seed, self.byte_len - oaep.hash_len() - 1);
+        // Step 2f
+        let mut masked_db = xor_vecs(&db, &db_mask);
+        // Step 2g
+        let seed_mask = oaep.mgf1(&masked_db, oaep.hash_len());
+        // Step 2h
+        let mut masked_seed = xor_vecs(&seed, &seed_mask);
+        // Step 2i
+        let mut em = Vec::new();
+        em.push(0);
+        em.append(&mut masked_seed);
+        em.append(&mut masked_db);
+        // Step 3a
+        let m_i = UCN::from_bytes(&em);
+        // Step 3b
+        let c_i = ep(&self.nu, &self.e, &m_i);
+        // Step 3c
+        let c = c_i.to_bytes(self.byte_len);
+        Ok(c)
+    }
 }