4 files changed, 89 insertions, 0 deletions
diff --git a/src/crypto/interface.cpp b/src/crypto/interface.cpp
index 2ae9c16..c11e382 100644
--- a/src/crypto/interface.cpp
+++ b/src/crypto/interface.cpp
@@ -68,6 +68,61 @@ void Interface::decrypt(EncryptedPacket& in, PlainPacket& out, const Buffer& mas
   out.setLength(len);
 }
 
+bool Interface::checkAndRemoveAuthTag(EncryptedPacket& packet, const Buffer& masterkey, const Buffer& mastersalt, role_t role)
+{
+  uint32_t digest_length = getDigestLength();
+  packet.withAuthTag(true);
+  if(!packet.getAuthTagLength()) {
+    return true;
+  }
+
+  Buffer digest(digest_length);
+  //Buffer key(masterkey.getLength(), false);
+  Buffer key(digest_length, false);
+  deriveKey(KD_INBOUND, LABEL_AUTH, role, packet.getSeqNr(), packet.getSeqNr(), packet.getMux(), masterkey, mastersalt, key);
+  //std::cout << "Interface::checkAndRemoveAuthTag: " << key.getHexDump() << std::endl;
+  calcAuthKey(key, digest,  packet.getAuthenticatedPortion(), packet.getAuthenticatedPortionLength() );
+
+  uint8_t* tag = packet.getAuthTag();
+  uint32_t length = (packet.getAuthTagLength() < digest_length) ? packet.getAuthTagLength() : digest_length;
+
+  if(length > digest_length)
+    for(uint32_t i=0; i < (packet.getAuthTagLength() - digest_length); ++i)
+      if(tag[i]) { return false; }
+
+  int ret = std::memcmp(&tag[packet.getAuthTagLength() - length], digest.getBuf() + digest_length - length, length);
+  packet.removeAuthTag();
+
+  if(ret) {
+    return false;
+  }
+
+  return true;
+}
+
+void Interface::addAuthTag(EncryptedPacket& packet, const Buffer& masterkey, const Buffer& mastersalt, role_t role)
+{
+  uint32_t digest_length = getDigestLength();
+  packet.addAuthTag();
+  if(!packet.getAuthTagLength()) {
+    return;
+  }
+  Buffer digest(digest_length);
+  //Buffer key(masterkey.getLength(), false);
+  Buffer key(digest_length, false);
+  deriveKey(KD_OUTBOUND, LABEL_AUTH, role, packet.getSeqNr(), packet.getSeqNr(), packet.getMux(), masterkey, mastersalt, key);
+  //std::cout << "Interface::addAuthTag: " << key.getHexDump() << std::endl;
+  calcAuthKey(key, digest,  packet.getAuthenticatedPortion(), packet.getAuthenticatedPortionLength() );
+  uint8_t* tag = packet.getAuthTag();
+  uint32_t length = (packet.getAuthTagLength() < digest_length) ? packet.getAuthTagLength() : digest_length;
+
+  if(length > digest_length) {
+    std::memset(tag, 0, packet.getAuthTagLength());
+  }
+
+  std::memcpy(&tag[packet.getAuthTagLength() - length], digest.getBuf() + digest_length - length, length);
+
+}
 
 satp_prf_label_t Interface::convertLabel(kd_dir_t dir, role_t role, satp_prf_label_t label)
 {
diff --git a/src/crypto/interface.h b/src/crypto/interface.h
index 0ca52fb..49013ba 100644
--- a/src/crypto/interface.h
+++ b/src/crypto/interface.h
@@ -118,6 +118,8 @@ namespace crypto {
     void decrypt(EncryptedPacket& in, PlainPacket& out, const Buffer& masterkey, const Buffer& mastersalt, role_t role);
     void calcCryptCtr(const Buffer& masterkey, const Buffer& mastersalt, kd_dir_t dir, role_t role, satp_prf_label_t label, seq_nr_t seq_nr, sender_id_t sender_id, mux_t mux, cipher_aesctr_ctr_t * ctr);
     void calcKeyCtr(const Buffer& mastersalt, kd_dir_t dir, role_t role, satp_prf_label_t label, seq_nr_t seq_nr, sender_id_t sender_id, mux_t mux, key_derivation_aesctr_ctr_t * ctr);
+    bool checkAndRemoveAuthTag(EncryptedPacket& packet, const Buffer& masterkey, const Buffer& mastersalt, role_t role);
+    void addAuthTag(EncryptedPacket& packet, const Buffer& masterkey, const Buffer& mastersalt, role_t role);
 
 
     // pure virtual
@@ -125,6 +127,8 @@ namespace crypto {
     virtual uint32_t cipher(uint8_t* in, uint32_t ilen, uint8_t* out, uint32_t olen, const Buffer& masterkey, const Buffer& mastersalt, role_t role, seq_nr_t seq_nr, sender_id_t sender_id, mux_t mux) = 0;
     virtual uint32_t decipher(uint8_t* in, uint32_t ilen, uint8_t* out, uint32_t olen, const Buffer& masterkey, const Buffer& mastersalt, role_t role, seq_nr_t seq_nr, sender_id_t sender_id, mux_t mux) = 0;
     virtual void deriveKey(kd_dir_t dir, satp_prf_label_t label, role_t role, seq_nr_t seq_nr, sender_id_t sender_id, mux_t mux, const Buffer& masterkey, const Buffer& mastersalt, Buffer& key) = 0;
+    virtual void calcAuthKey(Buffer & key, Buffer & digest, uint8_t * payload, size_t payload_length ) = 0;
+    virtual uint32_t getDigestLength() = 0;
 
     // virtual
     virtual ~Interface();
diff --git a/src/crypto/openssl.cpp b/src/crypto/openssl.cpp
index 9252b48..95ccf3e 100644
--- a/src/crypto/openssl.cpp
+++ b/src/crypto/openssl.cpp
@@ -47,6 +47,8 @@
 #include "../log.h"
 #include <openssl/aes.h>
 #include <openssl/sha.h>
+#include <openssl/hmac.h>
+
 #include "../anytunError.h"
 
 namespace crypto {
@@ -57,6 +59,26 @@ Openssl::~Openssl()
 }
 
 
+void Openssl::calcAuthKey(Buffer & key, Buffer & digest, uint8_t * payload, size_t payload_length )
+{
+  uint32_t digest_length = getDigestLength();
+  HMAC_CTX ctx;
+  HMAC_CTX_init(&ctx);
+  //HMAC_Init_ex(&ctx, NULL, 0, EVP_sha1(), NULL);
+
+  HMAC_Init_ex(&ctx, key.getBuf(), key.getLength(), EVP_sha1(), NULL);
+
+  uint8_t hmac[digest_length];
+  HMAC_Update(&ctx, payload, payload_length );
+  HMAC_Final(&ctx, hmac, NULL);
+
+  HMAC_CTX_cleanup(&ctx);
+  digest.setLength(digest_length);
+  
+  std::memcpy(digest.getBuf(), hmac, digest_length); 
+}
+
+
 void Openssl::calcMasterKeySalt(std::string passphrase, uint16_t length, Buffer& masterkey , Buffer& mastersalt)
 {
   cLog.msg(Log::PRIO_NOTICE) << "KeyDerivation: calculating master key from passphrase";
@@ -162,4 +184,9 @@ bool Openssl::init()
   return true;
 }
 
+uint32_t Openssl::getDigestLength()
+{
+  return 20;
+}
+
 }
diff --git a/src/crypto/openssl.h b/src/crypto/openssl.h
index 35a2d26..27ffd48 100644
--- a/src/crypto/openssl.h
+++ b/src/crypto/openssl.h
@@ -58,6 +58,9 @@ namespace crypto {
     virtual uint32_t cipher(uint8_t* in, uint32_t ilen, uint8_t* out, uint32_t olen, const Buffer& masterkey, const Buffer& mastersalt, role_t role, seq_nr_t seq_nr, sender_id_t sender_id, mux_t mux);
     virtual uint32_t decipher(uint8_t* in, uint32_t ilen, uint8_t* out, uint32_t olen, const Buffer& masterkey, const Buffer& mastersalt, role_t role, seq_nr_t seq_nr, sender_id_t sender_id, mux_t mux);
     virtual void deriveKey(kd_dir_t dir, satp_prf_label_t label, role_t role, seq_nr_t seq_nr, sender_id_t sender_id, mux_t mux, const Buffer& masterkey, const Buffer& mastersalt, Buffer& key);
+    virtual void calcAuthKey(Buffer & key, Buffer & digest, uint8_t * payload, size_t payload_length );
+    virtual uint32_t getDigestLength();
+
     // virtual
     virtual ~Openssl();
     virtual std::string printType();