allow encrypting in ctr mode from a given starting counter

2 files changed, 6 insertions, 1 deletions

diff --git a/src/aes.rs b/src/aes.rs
index 19a47cc..ffd40d9 100644
--- a/src/aes.rs
+++ b/src/aes.rs
@@ -52,10 +52,14 @@ pub fn encrypt_aes_128_cbc (bytes: &[u8], key: &[u8], iv: &[u8]) -> Vec<u8> {
 }
 
 pub fn aes_128_ctr (bytes: &[u8], key: &[u8], nonce: u64) -> Vec<u8> {
+    aes_128_ctr_with_counter(bytes, key, nonce, 0)
+}
+
+pub fn aes_128_ctr_with_counter (bytes: &[u8], key: &[u8], nonce: u64, counter_start: u64) -> Vec<u8> {
     let nonce_array: [u8; 8] = unsafe {
         ::std::mem::transmute(nonce.to_le())
     };
-    let mut counter = 0u64;
+    let mut counter = counter_start;
     let mut ret = vec![];
     for block in bytes.chunks(16) {
         let counter_array: [u8; 8] = unsafe {
diff --git a/src/lib.rs b/src/lib.rs
index eeb3278..2d6ebeb 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -16,6 +16,7 @@ pub use aes::decrypt_aes_128_cbc;
 pub use aes::encrypt_aes_128_ecb;
 pub use aes::encrypt_aes_128_cbc;
 pub use aes::aes_128_ctr;
+pub use aes::aes_128_ctr_with_counter;
 pub use base64::to_base64;
 pub use http::parse_query_string;
 pub use http::create_query_string;