Correct plaintext size limitation

Cosmian · Sep 20, 2022 · 3e92015 · 3e92015
1 parent c702042
commit 3e92015
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Showing 2 changed files with 7 additions and 6 deletions.
diff --git a/src/symmetric_crypto/aes_256_gcm_pure/mod.rs b/src/symmetric_crypto/aes_256_gcm_pure/mod.rs
@@ -24,8 +24,9 @@ const NONCE_LENGTH: usize = 12;
 /// Use a 128-bit MAC tag
 const MAC_LENGTH: usize = 16;
 
-/// A 96-bit nonce restricts the plaintext size to 4096 bytes
-const MAX_PLAINTEXT_LENGTH: usize = 4096;
+/// Plaintext size restriction from the NIST
+/// https://csrc.nist.gov/publications/detail/sp/800-38d/final
+const MAX_PLAINTEXT_LENGTH: u64 = (2u64.pow(39) - 256) / 8;
 
 /// Structure implementing `SymmetricCrypto` and the `DEM` interfaces based on
 /// AES 256 GCM.
@@ -47,7 +48,7 @@ impl Dem<KEY_LENGTH> for Aes256GcmCrypto {
         plaintext: &[u8],
         additional_data: Option<&[u8]>,
     ) -> Result<Vec<u8>, CryptoCoreError> {
-        if plaintext.len() > MAX_PLAINTEXT_LENGTH {
+        if plaintext.len() as u64 > MAX_PLAINTEXT_LENGTH {
             return Err(CryptoCoreError::InvalidSize(format!(
                 "Plaintext is too large ({} bytes), max size: {} ",
                 plaintext.len(),
@@ -79,11 +80,11 @@ impl Dem<KEY_LENGTH> for Aes256GcmCrypto {
                 Self::ENCRYPTION_OVERHEAD
             )));
         }
-        if ciphertext.len() > MAX_PLAINTEXT_LENGTH + Self::ENCRYPTION_OVERHEAD {
+        if ciphertext.len() as u64 > MAX_PLAINTEXT_LENGTH + Self::ENCRYPTION_OVERHEAD as u64 {
             return Err(CryptoCoreError::InvalidSize(format!(
                 "Ciphertext is too large ({} bytes), max size: {} ",
                 ciphertext.len(),
-                MAX_PLAINTEXT_LENGTH + Self::ENCRYPTION_OVERHEAD
+                MAX_PLAINTEXT_LENGTH + Self::ENCRYPTION_OVERHEAD as u64
             )));
         }
         // The ciphertext is of the form: nonce || AEAS ciphertext

diff --git a/src/symmetric_crypto/mod.rs b/src/symmetric_crypto/mod.rs
@@ -54,7 +54,7 @@ pub trait Dem<const KEY_LENGTH: usize>: Debug + PartialEq {
     ///
     /// - `rng`         : secure random number generator
     /// - `secret_key`  : secret symmetric key
-    /// - `plaintext`     : plaintext message
+    /// - `plaintext`   : plaintext message
     /// - `aad`         : optional data to use in the authentication method,
     /// must use the same for decryption
     fn encrypt<R: RngCore + CryptoRng>(