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analyzer/ssl: several improvements

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- use better data structures for secret and key material storage
- add documentation to the new methods in the analyzer
This commit is contained in:
Florian Wilkens 2021-06-24 17:05:34 +02:00
parent aaaff39e12
commit ebea26a065
3 changed files with 126 additions and 29 deletions
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59
src/analyzer/protocol/ssl/SSL.cc
View file

@ -50,9 +50,6 @@ SSL_Analyzer::SSL_Analyzer(Connection* c)
had_gap = false;
c_seq = 0;
s_seq = 0;
// FIXME: should this be initialized to nullptr?
secret = nullptr;
keys = nullptr;
pia = nullptr;
}
@ -136,14 +133,27 @@ void SSL_Analyzer::Undelivered(uint64_t seq, int len, bool orig)
interp->NewGap(orig, len);
}
void SSL_Analyzer::SetSecret(const u_char* data, int len)
void SSL_Analyzer::SetSecret(zeek::StringVal* secret)
{
secret = make_intrusive<zeek::StringVal>(len, (const char*)data);
SetSecret(secret->Len(), secret->Bytes());
}
void SSL_Analyzer::SetKeys(const u_char* data, int len)
void SSL_Analyzer::SetSecret(size_t len, const u_char* data)
{
keys = make_intrusive<zeek::StringVal>(len, (const char*)data);
secret.clear();
secret.append((const char*)data, len);
}
void SSL_Analyzer::SetKeys(zeek::StringVal* keys)
{
SetKeys(keys->Len(), keys->Bytes());
}
void SSL_Analyzer::SetKeys(size_t len, const u_char* data)
{
keys.clear();
keys.reserve(len);
std::copy(data, data + len, std::back_inserter(keys));
}
bool SSL_Analyzer::TLS12_PRF(const std::string& secret, const std::string& label,
@ -152,7 +162,7 @@ bool SSL_Analyzer::TLS12_PRF(const std::string& secret, const std::string& label
#ifdef OPENSSL_HAVE_KDF_H
// alloc buffers
EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_TLS1_PRF, NULL);
size_t seed_len = label.length() + rnd1_len + rnd2_len;
size_t seed_len = label.size() + rnd1_len + rnd2_len;
std::string seed{};
seed.reserve(seed_len);
@ -166,9 +176,9 @@ bool SSL_Analyzer::TLS12_PRF(const std::string& secret, const std::string& label
// FIXME: sha384 should not be hardcoded
if (EVP_PKEY_CTX_set_tls1_prf_md(pctx, EVP_sha384()) <= 0)
goto abort; /* Error */
if (EVP_PKEY_CTX_set1_tls1_prf_secret(pctx, secret.data(), secret.length()) <= 0)
if (EVP_PKEY_CTX_set1_tls1_prf_secret(pctx, secret.data(), secret.size()) <= 0)
goto abort; /* Error */
if (EVP_PKEY_CTX_add1_tls1_prf_seed(pctx, seed.data(), seed.length()) <= 0)
if (EVP_PKEY_CTX_add1_tls1_prf_seed(pctx, seed.data(), seed.size()) <= 0)
goto abort; /* Error */
if (EVP_PKEY_derive(pctx, out, &out_len) <= 0)
goto abort; /* Error */
@ -195,16 +205,16 @@ bool SSL_Analyzer::TryDecryptApplicationData(int len, const u_char* data, bool i
}
// Neither secret or key present: abort
if ( ( secret == nullptr || secret->Len() == 0 ) && ( keys == nullptr || keys->Len() == 0 ) )
if ( secret.size() == 0 && keys.size() == 0 )
{
DBG_LOG(DBG_ANALYZER, "Could not decrypt packet due to missing keys/secret.\n");
// FIXME: change util function to return a printably std::string for DBG_LOG
//print_hex("->client_random:", handshake_interp->client_random().data(), handshake_interp->client_random().length());
//print_hex("->client_random:", handshake_interp->client_random().data(), handshake_interp->client_random().size());
return false;
}
// Secret present, but no keys derived yet: derive keys
if ( secret != nullptr && secret->Len() != 0 && ( keys == nullptr || keys->Len() == 0 ) )
if ( secret.size() != 0 && keys.size() == 0 )
{
#ifdef OPENSSL_HAVE_KDF_H
DBG_LOG(DBG_ANALYZER, "Deriving TLS keys for connection foo");
@ -218,7 +228,7 @@ bool SSL_Analyzer::TryDecryptApplicationData(int len, const u_char* data, bool i
memcpy(crand, &(ts), 4);
memcpy(crand + 4, c_rnd.data(), c_rnd.length());
auto res = TLS12_PRF(secret->ToStdString(), "key expansion",
auto res = TLS12_PRF(secret, "key expansion",
(char*)s_rnd.data(), s_rnd.length(), crand, sizeof(crand), keybuf, sizeof(keybuf));
if ( !res )
{
@ -227,29 +237,36 @@ bool SSL_Analyzer::TryDecryptApplicationData(int len, const u_char* data, bool i
}
// save derived keys
SetKeys(keybuf, sizeof(keybuf));
SetKeys(sizeof(keybuf), keybuf);
#else
DBG_LOG(DBG_ANALYZER, "Cannot derive TLS keys as Zeek was compiled without <openssl/kdf.h>");
#endif
}
// Keys present: decrypt TLS application data
if ( keys != nullptr && keys->Len() == 72 )
if ( keys.size() == 72 )
{
// FIXME: could also print keys or conn id here
DBG_LOG(DBG_ANALYZER, "Decrypting application data");
// session keys & AEAD data
// client write_key
u_char c_wk[32];
// server write_key
u_char s_wk[32];
// client IV
u_char c_iv[4];
// server IV
u_char s_iv[4];
// AEAD nonce & tag
u_char s_aead_nonce[12];
u_char s_aead_tag[13];
memcpy(c_wk, keys->Bytes(), 32);
memcpy(s_wk, &(keys->Bytes()[32]), 32);
memcpy(c_iv, &(keys->Bytes()[64]), 4);
memcpy(s_iv, &(keys->Bytes()[68]), 4);
// FIXME: there should be a better way to do these copies
memcpy(c_wk, keys.data(), 32);
memcpy(s_wk, keys.data() + 32, 32);
memcpy(c_iv, keys.data() + 64, 4);
memcpy(s_iv, keys.data() + 68, 4);
// FIXME: should we change types here?
u_char* encrypted = (u_char*)data;

90
src/analyzer/protocol/ssl/SSL.h
View file

@ -34,12 +34,92 @@ public:
static analyzer::Analyzer* Instantiate(Connection* conn)
{ return new SSL_Analyzer(conn); }
// Key material for decryption
void SetSecret(const u_char* data, int len);
void SetKeys(const u_char* data, int len);
/**
* Set the secret that should be used to derive keys for the
* connection. (For TLS 1.2 this is the pre-master secret)
*
* @param secret The secret to set
*/
void SetSecret(StringVal* secret);
/**
* Set the secret that should be used to derive keys for the
* connection. (For TLS 1.2 this is the pre-master secret)
*
* @param len Length of the secret bytes
*
* @param data Pointer to the secret bytes
*/
void SetSecret(size_t len, const u_char* data);
/**
* Set the decryption keys that should be used to decrypt
* TLS application data in the connection.
*
* @param keys The key buffer as derived via TLS PRF (for
* AES_GCM this should be 72 bytes in length)
*/
void SetKeys(StringVal* keys);
/**
* Set the decryption keys that should be used to decrypt
* TLS application data in the connection.
*
* @param len Length of the key buffer (for AES_GCM this should
* be 72)
*
* @param data Pointer to the key buffer as derived via TLS PRF
*/
void SetKeys(size_t len, const u_char* data);
/**
* Try to decrypt TLS application data from a packet. Requires secret or keys to be set prior
*
* @param len Length of the encrypted bytes to decrypt
*
* @param data Pointer to the encrypted bytes to decrypt
*
* @param is_orig Direction of the connection
*
* @param content_type Content type as given in the TLS packet
*
* @param raw_tls_version Raw TLS version as given in the TLS packets
*/
bool TryDecryptApplicationData(int len, const u_char* data, bool is_orig, uint8_t content_type, uint16_t raw_tls_version);
/**
* TLS 1.2 pseudo random function (PRF) used to expand the pre-master secret and derive keys.
* The seed is obtained by concatinating rnd1 and rnd2
*
* @param secret Secret as defined in the TLS RFC
*
* @param label Label as defined in the TLS RFC
*
* @param rnd1 Pointer to the first part of the seed
*
* @param rnd1_len Length of the first part of the seed
*
* @param rnd2 Pointer to the second part of the seed
*
* @param rnd2_len Length of the second part of the seed
*
* @param out Pointer to the derived bytes
*
* @param out_len Length indicating how many bytes should be derived
*
* @return True, if the operation completed successfully, false otherwise
*/
bool TLS12_PRF(const std::string& secret, const std::string& label, const char* rnd1, size_t rnd1_len, const char* rnd2, size_t rnd2_len, u_char* out, size_t out_len);
/**
* Forward decrypted TLS application data to child analyzers
*
* @param len Length of the data to forward
*
* @param data Pointer to the data to forward
*
* @param is_orig Direction of the connection
*/
void ForwardDecryptedData(int len, const u_char* data, bool is_orig);
protected:
@ -50,8 +130,8 @@ protected:
// FIXME: should this be moved into the connection?
int c_seq;
int s_seq;
StringValPtr secret;
StringValPtr keys;
std::string secret;
std::vector<u_char> keys;
zeek::analyzer::pia::PIA_TCP *pia;
};

4
src/analyzer/protocol/ssl/functions.bif
View file

@ -22,7 +22,7 @@ function set_secret%(c: connection, secret: string%): bool
analyzer::Analyzer* sa = c->FindAnalyzer("SSL");
if ( sa )
{
static_cast<zeek::analyzer::ssl::SSL_Analyzer*>(sa)->SetSecret(secret->Bytes(), secret->Len());
static_cast<zeek::analyzer::ssl::SSL_Analyzer*>(sa)->SetSecret(secret);
return zeek::val_mgr->True();
}
return zeek::val_mgr->False();
@ -33,7 +33,7 @@ function set_keys%(c: connection, keys: string%): bool
analyzer::Analyzer* sa = c->FindAnalyzer("SSL");
if ( sa )
{
static_cast<zeek::analyzer::ssl::SSL_Analyzer*>(sa)->SetKeys(keys->Bytes(), keys->Len());
static_cast<zeek::analyzer::ssl::SSL_Analyzer*>(sa)->SetKeys(keys);
return zeek::val_mgr->True();
}
return zeek::val_mgr->False();