aboutsummaryrefslogtreecommitdiff
path: root/src/aes_ctr.rs
diff options
context:
space:
mode:
Diffstat (limited to 'src/aes_ctr.rs')
-rw-r--r--src/aes_ctr.rs281
1 files changed, 281 insertions, 0 deletions
diff --git a/src/aes_ctr.rs b/src/aes_ctr.rs
new file mode 100644
index 0000000..0f34335
--- /dev/null
+++ b/src/aes_ctr.rs
@@ -0,0 +1,281 @@
+//! A counter mode (CTR) for AES to work with the encryption used in zip files.
+//!
+//! This was implemented since the zip specification requires the mode to not use a nonce and uses a
+//! different byte order (little endian) than NIST (big endian).
+//! See [AesCtrZipKeyStream](./struct.AesCtrZipKeyStream.html) for more information.
+
+use aes::cipher::generic_array::GenericArray;
+use aes::{BlockEncrypt, NewBlockCipher};
+use byteorder::WriteBytesExt;
+use std::{any, fmt};
+
+/// Internal block size of an AES cipher.
+const AES_BLOCK_SIZE: usize = 16;
+
+/// AES-128.
+#[derive(Debug)]
+pub struct Aes128;
+/// AES-192
+#[derive(Debug)]
+pub struct Aes192;
+/// AES-256.
+#[derive(Debug)]
+pub struct Aes256;
+
+/// An AES cipher kind.
+pub trait AesKind {
+ /// Key type.
+ type Key: AsRef<[u8]>;
+ /// Cipher used to decrypt.
+ type Cipher;
+}
+
+impl AesKind for Aes128 {
+ type Key = [u8; 16];
+ type Cipher = aes::Aes128;
+}
+
+impl AesKind for Aes192 {
+ type Key = [u8; 24];
+ type Cipher = aes::Aes192;
+}
+
+impl AesKind for Aes256 {
+ type Key = [u8; 32];
+ type Cipher = aes::Aes256;
+}
+
+/// An AES-CTR key stream generator.
+///
+/// Implements the slightly non-standard AES-CTR variant used by WinZip AES encryption.
+///
+/// Typical AES-CTR implementations combine a nonce with a 64 bit counter. WinZIP AES instead uses
+/// no nonce and also uses a different byte order (little endian) than NIST (big endian).
+///
+/// The stream implements the `Read` trait; encryption or decryption is performed by XOR-ing the
+/// bytes from the key stream with the ciphertext/plaintext.
+pub struct AesCtrZipKeyStream<C: AesKind> {
+ /// Current AES counter.
+ counter: u128,
+ /// AES cipher instance.
+ cipher: C::Cipher,
+ /// Stores the currently available keystream bytes.
+ buffer: [u8; AES_BLOCK_SIZE],
+ /// Number of bytes already used up from `buffer`.
+ pos: usize,
+}
+
+impl<C> fmt::Debug for AesCtrZipKeyStream<C>
+where
+ C: AesKind,
+{
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ write!(
+ f,
+ "AesCtrZipKeyStream<{}>(counter: {})",
+ any::type_name::<C>(),
+ self.counter
+ )
+ }
+}
+
+impl<C> AesCtrZipKeyStream<C>
+where
+ C: AesKind,
+ C::Cipher: NewBlockCipher,
+{
+ /// Creates a new zip variant AES-CTR key stream.
+ ///
+ /// # Panics
+ ///
+ /// This panics if `key` doesn't have the correct size for cipher `C`.
+ pub fn new(key: &[u8]) -> AesCtrZipKeyStream<C> {
+ AesCtrZipKeyStream {
+ counter: 1,
+ cipher: C::Cipher::new(GenericArray::from_slice(key)),
+ buffer: [0u8; AES_BLOCK_SIZE],
+ pos: AES_BLOCK_SIZE,
+ }
+ }
+}
+
+impl<C> AesCipher for AesCtrZipKeyStream<C>
+where
+ C: AesKind,
+ C::Cipher: BlockEncrypt,
+{
+ /// Decrypt or encrypt `target`.
+ #[inline]
+ fn crypt_in_place(&mut self, mut target: &mut [u8]) {
+ while !target.is_empty() {
+ if self.pos == AES_BLOCK_SIZE {
+ // Note: AES block size is always 16 bytes, same as u128.
+ self.buffer
+ .as_mut()
+ .write_u128::<byteorder::LittleEndian>(self.counter)
+ .expect("did not expect u128 le conversion to fail");
+ self.cipher
+ .encrypt_block(GenericArray::from_mut_slice(&mut self.buffer));
+ self.counter += 1;
+ self.pos = 0;
+ }
+
+ let target_len = target.len().min(AES_BLOCK_SIZE - self.pos);
+
+ xor(
+ &mut target[0..target_len],
+ &self.buffer[self.pos..(self.pos + target_len)],
+ );
+ target = &mut target[target_len..];
+ self.pos += target_len;
+ }
+ }
+}
+
+/// This trait allows using generic AES ciphers with different key sizes.
+pub trait AesCipher {
+ fn crypt_in_place(&mut self, target: &mut [u8]);
+}
+
+/// XORs a slice in place with another slice.
+#[inline]
+fn xor(dest: &mut [u8], src: &[u8]) {
+ assert_eq!(dest.len(), src.len());
+
+ for (lhs, rhs) in dest.iter_mut().zip(src.iter()) {
+ *lhs ^= *rhs;
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use super::{Aes128, Aes192, Aes256, AesCipher, AesCtrZipKeyStream, AesKind};
+ use aes::{BlockEncrypt, NewBlockCipher};
+
+ /// Checks whether `crypt_in_place` produces the correct plaintext after one use and yields the
+ /// cipertext again after applying it again.
+ fn roundtrip<Aes>(key: &[u8], ciphertext: &mut [u8], expected_plaintext: &[u8])
+ where
+ Aes: AesKind,
+ Aes::Cipher: NewBlockCipher + BlockEncrypt,
+ {
+ let mut key_stream = AesCtrZipKeyStream::<Aes>::new(key);
+
+ let mut plaintext: Vec<u8> = ciphertext.to_vec();
+ key_stream.crypt_in_place(plaintext.as_mut_slice());
+ assert_eq!(plaintext, expected_plaintext.to_vec());
+
+ // Round-tripping should yield the ciphertext again.
+ let mut key_stream = AesCtrZipKeyStream::<Aes>::new(key);
+ key_stream.crypt_in_place(&mut plaintext);
+ assert_eq!(plaintext, ciphertext.to_vec());
+ }
+
+ #[test]
+ #[should_panic]
+ fn new_with_wrong_key_size() {
+ AesCtrZipKeyStream::<Aes128>::new(&[1, 2, 3, 4, 5]);
+ }
+
+ // The data used in these tests was generated with p7zip without any compression.
+ // It's not possible to recreate the exact same data, since a random salt is used for encryption.
+ // `7z a -phelloworld -mem=AES256 -mx=0 aes256_40byte.zip 40byte_data.txt`
+ #[test]
+ fn crypt_aes_256_0_byte() {
+ let mut ciphertext = [];
+ let expected_plaintext = &[];
+ let key = [
+ 0x0b, 0xec, 0x2e, 0xf2, 0x46, 0xf0, 0x7e, 0x35, 0x16, 0x54, 0xe0, 0x98, 0x10, 0xb3,
+ 0x18, 0x55, 0x24, 0xa3, 0x9e, 0x0e, 0x40, 0xe7, 0x92, 0xad, 0xb2, 0x8a, 0x48, 0xf4,
+ 0x5c, 0xd0, 0xc0, 0x54,
+ ];
+
+ roundtrip::<Aes256>(&key, &mut ciphertext, expected_plaintext);
+ }
+
+ #[test]
+ fn crypt_aes_128_5_byte() {
+ let mut ciphertext = [0x98, 0xa9, 0x8c, 0x26, 0x0e];
+ let expected_plaintext = b"asdf\n";
+ let key = [
+ 0xe0, 0x25, 0x7b, 0x57, 0x97, 0x6a, 0xa4, 0x23, 0xab, 0x94, 0xaa, 0x44, 0xfd, 0x47,
+ 0x4f, 0xa5,
+ ];
+
+ roundtrip::<Aes128>(&key, &mut ciphertext, expected_plaintext);
+ }
+
+ #[test]
+ fn crypt_aes_192_5_byte() {
+ let mut ciphertext = [0x36, 0x55, 0x5c, 0x61, 0x3c];
+ let expected_plaintext = b"asdf\n";
+ let key = [
+ 0xe4, 0x4a, 0x88, 0x52, 0x8f, 0xf7, 0x0b, 0x81, 0x7b, 0x75, 0xf1, 0x74, 0x21, 0x37,
+ 0x8c, 0x90, 0xad, 0xbe, 0x4a, 0x65, 0xa8, 0x96, 0x0e, 0xcc,
+ ];
+
+ roundtrip::<Aes192>(&key, &mut ciphertext, expected_plaintext);
+ }
+
+ #[test]
+ fn crypt_aes_256_5_byte() {
+ let mut ciphertext = [0xc2, 0x47, 0xc0, 0xdc, 0x56];
+ let expected_plaintext = b"asdf\n";
+ let key = [
+ 0x79, 0x5e, 0x17, 0xf2, 0xc6, 0x3d, 0x28, 0x9b, 0x4b, 0x4b, 0xbb, 0xa9, 0xba, 0xc9,
+ 0xa5, 0xee, 0x3a, 0x4f, 0x0f, 0x4b, 0x29, 0xbd, 0xe9, 0xb8, 0x41, 0x9c, 0x41, 0xa5,
+ 0x15, 0xb2, 0x86, 0xab,
+ ];
+
+ roundtrip::<Aes256>(&key, &mut ciphertext, expected_plaintext);
+ }
+
+ #[test]
+ fn crypt_aes_128_40_byte() {
+ let mut ciphertext = [
+ 0xcf, 0x72, 0x6b, 0xa1, 0xb2, 0x0f, 0xdf, 0xaa, 0x10, 0xad, 0x9c, 0x7f, 0x6d, 0x1c,
+ 0x8d, 0xb5, 0x16, 0x7e, 0xbb, 0x11, 0x69, 0x52, 0x8c, 0x89, 0x80, 0x32, 0xaa, 0x76,
+ 0xa6, 0x18, 0x31, 0x98, 0xee, 0xdd, 0x22, 0x68, 0xb7, 0xe6, 0x77, 0xd2,
+ ];
+ let expected_plaintext = b"Lorem ipsum dolor sit amet, consectetur\n";
+ let key = [
+ 0x43, 0x2b, 0x6d, 0xbe, 0x05, 0x76, 0x6c, 0x9e, 0xde, 0xca, 0x3b, 0xf8, 0xaf, 0x5d,
+ 0x81, 0xb6,
+ ];
+
+ roundtrip::<Aes128>(&key, &mut ciphertext, expected_plaintext);
+ }
+
+ #[test]
+ fn crypt_aes_192_40_byte() {
+ let mut ciphertext = [
+ 0xa6, 0xfc, 0x52, 0x79, 0x2c, 0x6c, 0xfe, 0x68, 0xb1, 0xa8, 0xb3, 0x07, 0x52, 0x8b,
+ 0x82, 0xa6, 0x87, 0x9c, 0x72, 0x42, 0x3a, 0xf8, 0xc6, 0xa9, 0xc9, 0xfb, 0x61, 0x19,
+ 0x37, 0xb9, 0x56, 0x62, 0xf4, 0xfc, 0x5e, 0x7a, 0xdd, 0x55, 0x0a, 0x48,
+ ];
+ let expected_plaintext = b"Lorem ipsum dolor sit amet, consectetur\n";
+ let key = [
+ 0xac, 0x92, 0x41, 0xba, 0xde, 0xd9, 0x02, 0xfe, 0x40, 0x92, 0x20, 0xf6, 0x56, 0x03,
+ 0xfe, 0xae, 0x1b, 0xba, 0x01, 0x97, 0x97, 0x79, 0xbb, 0xa6,
+ ];
+
+ roundtrip::<Aes192>(&key, &mut ciphertext, expected_plaintext);
+ }
+
+ #[test]
+ fn crypt_aes_256_40_byte() {
+ let mut ciphertext = [
+ 0xa9, 0x99, 0xbd, 0xea, 0x82, 0x9b, 0x8f, 0x2f, 0xb7, 0x52, 0x2f, 0x6b, 0xd8, 0xf6,
+ 0xab, 0x0e, 0x24, 0x51, 0x9e, 0x18, 0x0f, 0xc0, 0x8f, 0x54, 0x15, 0x80, 0xae, 0xbc,
+ 0xa0, 0x5c, 0x8a, 0x11, 0x8d, 0x14, 0x7e, 0xc5, 0xb4, 0xae, 0xd3, 0x37,
+ ];
+ let expected_plaintext = b"Lorem ipsum dolor sit amet, consectetur\n";
+ let key = [
+ 0x64, 0x7c, 0x7a, 0xde, 0xf0, 0xf2, 0x61, 0x49, 0x1c, 0xf1, 0xf1, 0xe3, 0x37, 0xfc,
+ 0xe1, 0x4d, 0x4a, 0x77, 0xd4, 0xeb, 0x9e, 0x3d, 0x75, 0xce, 0x9a, 0x3e, 0x10, 0x50,
+ 0xc2, 0x07, 0x36, 0xb6,
+ ];
+
+ roundtrip::<Aes256>(&key, &mut ciphertext, expected_plaintext);
+ }
+}
generated by cgit v1.2.3 (git 2.25.1) at 2024-06-24 17:57:38 +0000