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Document SSL_Cipher::setIVec

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This commit is contained in:
Jakob Unterwurzacher 2014-11-23 21:19:25 +01:00
parent 43a1cd3344
commit 3fce933f65
1 changed files with 27 additions and 6 deletions
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33
encfs/SSL_Cipher.cpp
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@ -49,14 +49,14 @@ using namespace rel;
using namespace rlog;
const int MAX_KEYLENGTH = 32; // in bytes (256 bit)
const int MAX_IVLENGTH = 16;
const int MAX_IVLENGTH = 16; // 128 bit (AES block size, Blowfish has 64)
const int KEY_CHECKSUM_BYTES = 4;
#ifndef MIN
inline int MIN(int a, int b) { return (a < b) ? a : b; }
#endif
/*
/**
This produces the same result as OpenSSL's EVP_BytesToKey. The difference
is that here we can explicitly specify the key size, instead of relying on
the state of EVP_CIPHER struct. EVP_BytesToKey will only produce 128 bit
@ -348,7 +348,7 @@ SSL_Cipher::~SSL_Cipher() {}
Interface SSL_Cipher::interface() const { return realIface; }
/*
/**
create a key from the password.
Use SHA to distribute entropy from the password into the key.
@ -413,7 +413,7 @@ CipherKey SSL_Cipher::newKey(const char *password, int passwdLength) {
return key;
}
/*
/**
Create a random key.
We use the OpenSSL library to generate random bytes, then take the hash of
those bytes to use as the key.
@ -447,7 +447,7 @@ CipherKey SSL_Cipher::newRandomKey() {
return key;
}
/*
/**
compute a 64-bit check value for the data using HMAC.
*/
static uint64_t _checksum_64(SSLKey *key, const unsigned char *data,
@ -487,6 +487,11 @@ static uint64_t _checksum_64(SSLKey *key, const unsigned char *data,
return value;
}
/**
* Write "len" bytes of random data into "buf"
*
* See "man 3 RAND_bytes" for the effect of strongRandom
*/
bool SSL_Cipher::randomize(unsigned char *buf, int len,
bool strongRandom) const {
// to avoid warnings of uninitialized data from valgrind
@ -604,6 +609,22 @@ int SSL_Cipher::cipherBlockSize() const {
return EVP_CIPHER_block_size(_blockCipher);
}
/**
* Generate the initialization vector that will actually be used for
* AES/Blowfish encryption and decryption in {stream,block}{Encode,Decode}
*
* It is derived from
* 1) a "seed" value that is passed from the higher layer, for the default
* configuration it is "block_number XOR per_file_IV_header" from
* CipherFileIO
* 2) The IV that is used for encrypting the master key, "IVData(key)"
* 3) The master key
* using
* ivec = HMAC(master_key, IVData(key) CONCAT seed)
*
* As an HMAC is unpredictable as long as the key is secret, the only
* requirement for "seed" is that is must be unique.
*/
void SSL_Cipher::setIVec(unsigned char *ivec, uint64_t seed,
const shared_ptr<SSLKey> &key) const {
if (iface.current() >= 3) {
@ -695,7 +716,7 @@ static void unshuffleBytes(unsigned char *buf, int size) {
for (int i = size - 1; i; --i) buf[i] ^= buf[i - 1];
}
/* Partial blocks are encoded with a stream cipher. We make multiple passes on
/** Partial blocks are encoded with a stream cipher. We make multiple passes on
the data to ensure that the ends of the data depend on each other.
*/
bool SSL_Cipher::streamEncode(unsigned char *buf, int size, uint64_t iv64,