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crypto: add AES 128/256 CBC classes

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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).
This commit is contained in:
Cory Fields 2015-03-20 00:49:13 -04:00 committed by Pieter Wuille
parent 6bec172eb9
commit 27a212dcb4
2 changed files with 196 additions and 0 deletions
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144
src/crypto/aes.cpp
View file

@ -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);
}

52
src/crypto/aes.h
View file

@ -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