crypto: add AES 128/256 CBC classes

The output should always match openssl's, even for failed operations. Even for
a decrypt with broken padding, the output is always deterministic (and attemtps
to be constant-time).

src/crypto/aes.cpp

@@ -71,3 +71,147 @@ void AES256Decrypt::Decrypt(unsigned char plaintext[16], const unsigned char cip
 {
     AES256_decrypt(&ctx, 1, plaintext, ciphertext);
 }
+
+
+template <typename T>
+static int CBCEncrypt(const T& enc, const unsigned char iv[AES_BLOCKSIZE], const unsigned char* data, int size, bool pad, unsigned char* out)
+{
+    int written = 0;
+    int padsize = size % AES_BLOCKSIZE;
+    unsigned char mixed[AES_BLOCKSIZE];
+
+    if (!data || !size || !out)
+        return 0;
+
+    if (!pad && padsize != 0)
+        return 0;
+
+    memcpy(mixed, iv, AES_BLOCKSIZE);
+
+    // Write all but the last block
+    while (written + AES_BLOCKSIZE <= size) {
+        for (int i = 0; i != AES_BLOCKSIZE; i++)
+            mixed[i] ^= *data++;
+        enc.Encrypt(out + written, mixed);
+        memcpy(mixed, out + written, AES_BLOCKSIZE);
+        written += AES_BLOCKSIZE;
+    }
+    if (pad) {
+        // For all that remains, pad each byte with the value of the remaining
+        // space. If there is none, pad by a full block.
+        for (int i = 0; i != padsize; i++)
+            mixed[i] ^= *data++;
+        for (int i = padsize; i != AES_BLOCKSIZE; i++)
+            mixed[i] ^= AES_BLOCKSIZE - padsize;
+        enc.Encrypt(out + written, mixed);
+        written += AES_BLOCKSIZE;
+    }
+    return written;
+}
+
+template <typename T>
+static int CBCDecrypt(const T& dec, const unsigned char iv[AES_BLOCKSIZE], const unsigned char* data, int size, bool pad, unsigned char* out)
+{
+    unsigned char padsize = 0;
+    int written = 0;
+    bool fail = false;
+    const unsigned char* prev = iv;
+
+    if (!data || !size || !out)
+        return 0;
+
+    if (size % AES_BLOCKSIZE != 0)
+        return 0;
+
+    // Decrypt all data. Padding will be checked in the output.
+    while (written != size) {
+        dec.Decrypt(out, data + written);
+        for (int i = 0; i != AES_BLOCKSIZE; i++)
+            *out++ ^= prev[i];
+        prev = data + written;
+        written += AES_BLOCKSIZE;
+    }
+
+    // When decrypting padding, attempt to run in constant-time
+    if (pad) {
+        // If used, padding size is the value of the last decrypted byte. For
+        // it to be valid, It must be between 1 and AES_BLOCKSIZE.
+        padsize = *--out;
+        fail = !padsize | (padsize > AES_BLOCKSIZE);
+
+        // If not well-formed, treat it as though there's no padding.
+        padsize *= !fail;
+
+        // All padding must equal the last byte otherwise it's not well-formed
+        for (int i = AES_BLOCKSIZE; i != 0; i--)
+            fail |= ((i > AES_BLOCKSIZE - padsize) & (*out-- != padsize));
+
+        written -= padsize;
+    }
+    return written * !fail;
+}
+
+AES256CBCEncrypt::AES256CBCEncrypt(const unsigned char key[AES256_KEYSIZE], const unsigned char ivIn[AES_BLOCKSIZE], bool padIn)
+    : enc(key), pad(padIn)
+{
+    memcpy(iv, ivIn, AES_BLOCKSIZE);
+}
+
+int AES256CBCEncrypt::Encrypt(const unsigned char* data, int size, unsigned char* out) const
+{
+    return CBCEncrypt(enc, iv, data, size, pad, out);
+}
+
+AES256CBCEncrypt::~AES256CBCEncrypt()
+{
+    memset(iv, 0, sizeof(iv));
+}
+
+AES256CBCDecrypt::AES256CBCDecrypt(const unsigned char key[AES256_KEYSIZE], const unsigned char ivIn[AES_BLOCKSIZE], bool padIn)
+    : dec(key), pad(padIn)
+{
+    memcpy(iv, ivIn, AES_BLOCKSIZE);
+}
+
+
+int AES256CBCDecrypt::Decrypt(const unsigned char* data, int size, unsigned char* out) const
+{
+    return CBCDecrypt(dec, iv, data, size, pad, out);
+}
+
+AES256CBCDecrypt::~AES256CBCDecrypt()
+{
+    memset(iv, 0, sizeof(iv));
+}
+
+AES128CBCEncrypt::AES128CBCEncrypt(const unsigned char key[AES128_KEYSIZE], const unsigned char ivIn[AES_BLOCKSIZE], bool padIn)
+    : enc(key), pad(padIn)
+{
+    memcpy(iv, ivIn, AES_BLOCKSIZE);
+}
+
+AES128CBCEncrypt::~AES128CBCEncrypt()
+{
+    memset(iv, 0, AES_BLOCKSIZE);
+}
+
+int AES128CBCEncrypt::Encrypt(const unsigned char* data, int size, unsigned char* out) const
+{
+    return CBCEncrypt(enc, iv, data, size, pad, out);
+}
+
+AES128CBCDecrypt::AES128CBCDecrypt(const unsigned char key[AES128_KEYSIZE], const unsigned char ivIn[AES_BLOCKSIZE], bool padIn)
+    : dec(key), pad(padIn)
+{
+    memcpy(iv, ivIn, AES_BLOCKSIZE);
+}
+
+AES128CBCDecrypt::~AES128CBCDecrypt()
+{
+    memset(iv, 0, AES_BLOCKSIZE);
+}
+
+int AES128CBCDecrypt::Decrypt(const unsigned char* data, int size, unsigned char* out) const
+{
+    return CBCDecrypt(dec, iv, data, size, pad, out);
+}

src/crypto/aes.h

@@ -63,4 +63,56 @@ public:
     void Decrypt(unsigned char plaintext[16], const unsigned char ciphertext[16]) const;
 };
 
+class AES256CBCEncrypt
+{
+public:
+    AES256CBCEncrypt(const unsigned char key[AES256_KEYSIZE], const unsigned char ivIn[AES_BLOCKSIZE], bool padIn);
+    ~AES256CBCEncrypt();
+    int Encrypt(const unsigned char* data, int size, unsigned char* out) const;
+
+private:
+    const AES256Encrypt enc;
+    const bool pad;
+    unsigned char iv[AES_BLOCKSIZE];
+};
+
+class AES256CBCDecrypt
+{
+public:
+    AES256CBCDecrypt(const unsigned char key[AES256_KEYSIZE], const unsigned char ivIn[AES_BLOCKSIZE], bool padIn);
+    ~AES256CBCDecrypt();
+    int Decrypt(const unsigned char* data, int size, unsigned char* out) const;
+
+private:
+    const AES256Decrypt dec;
+    const bool pad;
+    unsigned char iv[AES_BLOCKSIZE];
+};
+
+class AES128CBCEncrypt
+{
+public:
+    AES128CBCEncrypt(const unsigned char key[AES128_KEYSIZE], const unsigned char ivIn[AES_BLOCKSIZE], bool padIn);
+    ~AES128CBCEncrypt();
+    int Encrypt(const unsigned char* data, int size, unsigned char* out) const;
+
+private:
+    const AES128Encrypt enc;
+    const bool pad;
+    unsigned char iv[AES_BLOCKSIZE];
+};
+
+class AES128CBCDecrypt
+{
+public:
+    AES128CBCDecrypt(const unsigned char key[AES128_KEYSIZE], const unsigned char ivIn[AES_BLOCKSIZE], bool padIn);
+    ~AES128CBCDecrypt();
+    int Decrypt(const unsigned char* data, int size, unsigned char* out) const;
+
+private:
+    const AES128Decrypt dec;
+    const bool pad;
+    unsigned char iv[AES_BLOCKSIZE];
+};
+
 #endif // BITCOIN_CRYPTO_AES_H