From aae9ec0492d281c419f94a436d8f4f301bc8f5dd Mon Sep 17 00:00:00 2001 From: Davide Beatrici Date: Sat, 3 Nov 2018 15:14:56 +0100 Subject: [PATCH 1/3] Mayaqua/Encrypt: add CipherProcessAead() function to encrypt/decrypt with AEAD ciphers --- src/Mayaqua/Encrypt.c | 69 +++++++++++++++++++++++++++++++++++++++++++ src/Mayaqua/Encrypt.h | 5 +++- 2 files changed, 73 insertions(+), 1 deletion(-) diff --git a/src/Mayaqua/Encrypt.c b/src/Mayaqua/Encrypt.c index 9d2c1a0d..b59ff886 100644 --- a/src/Mayaqua/Encrypt.c +++ b/src/Mayaqua/Encrypt.c @@ -570,6 +570,7 @@ CIPHER *NewCipher(char *name) EVP_CIPHER_CTX_init(c->Ctx); #endif + c->IsAeadCipher = EVP_CIPHER_flags(c->Cipher) & EVP_CIPH_FLAG_AEAD_CIPHER; c->BlockSize = EVP_CIPHER_block_size(c->Cipher); c->KeySize = EVP_CIPHER_key_length(c->Cipher); c->IvSize = EVP_CIPHER_iv_length(c->Cipher); @@ -634,6 +635,74 @@ UINT CipherProcess(CIPHER *c, void *iv, void *dest, void *src, UINT size) return r + r2; } +// Process encryption / decryption (AEAD) +UINT CipherProcessAead(CIPHER *c, void *iv, void *tag, UINT tag_size, void *dest, void *src, UINT src_size, void *aad, UINT aad_size) +{ + int r = src_size; + int r2 = 0; + // Validate arguments + if (c == NULL) + { + return 0; + } + else if (c->IsNullCipher) + { + Copy(dest, src, src_size); + return src_size; + } + else if (c->IsAeadCipher == false || iv == NULL || tag == NULL || tag_size == 0 || dest == NULL || src == NULL || src_size == 0) + { + return 0; + } + + if (EVP_CipherInit_ex(c->Ctx, NULL, NULL, NULL, iv, c->Encrypt) == false) + { + Debug("CipherProcessAead(): EVP_CipherInit_ex() failed with error: %s\n", OpenSSL_Error()); + return 0; + } + + if (c->Encrypt == false) + { + if (EVP_CIPHER_CTX_ctrl(c->Ctx, EVP_CTRL_AEAD_SET_TAG, tag_size, tag) == false) + { + Debug("CipherProcessAead(): EVP_CIPHER_CTX_ctrl() failed to set the tag!\n"); + return 0; + } + } + + if (aad != NULL && aad_size != 0) + { + if (EVP_CipherUpdate(c->Ctx, NULL, &r, aad, aad_size) == false) + { + Debug("CipherProcessAead(): EVP_CipherUpdate() failed with error: %s\n", OpenSSL_Error()); + return 0; + } + } + + if (EVP_CipherUpdate(c->Ctx, dest, &r, src, src_size) == false) + { + Debug("CipherProcessAead(): EVP_CipherUpdate() failed with error: %s\n", OpenSSL_Error()); + return 0; + } + + if (EVP_CipherFinal_ex(c->Ctx, ((UCHAR *)dest) + (UINT)r, &r2) == false) + { + Debug("CipherProcessAead(): EVP_CipherFinal_ex() failed with error: %s\n", OpenSSL_Error()); + return 0; + } + + if (c->Encrypt) + { + if (EVP_CIPHER_CTX_ctrl(c->Ctx, EVP_CTRL_AEAD_GET_TAG, tag_size, tag) == false) + { + Debug("CipherProcessAead(): EVP_CIPHER_CTX_ctrl() failed to get the tag!\n"); + return 0; + } + } + + return r + r2; +} + // Release of the cipher object void FreeCipher(CIPHER *c) { diff --git a/src/Mayaqua/Encrypt.h b/src/Mayaqua/Encrypt.h index 1b2c0ff9..1a9bb468 100644 --- a/src/Mayaqua/Encrypt.h +++ b/src/Mayaqua/Encrypt.h @@ -239,6 +239,8 @@ void RAND_Free_For_SoftEther(); // OpenSSL <1.1 Shims #if OPENSSL_VERSION_NUMBER < 0x10100000L +# define EVP_CTRL_AEAD_GET_TAG EVP_CTRL_GCM_GET_TAG +# define EVP_CTRL_AEAD_SET_TAG EVP_CTRL_GCM_SET_TAG # define EVP_PKEY_get0_RSA(obj) ((obj)->pkey.rsa) # define EVP_PKEY_base_id(pkey) ((pkey)->type) # define X509_get0_notBefore(x509) ((x509)->cert_info->validity->notBefore) @@ -348,7 +350,7 @@ struct DH_CTX struct CIPHER { char Name[MAX_PATH]; - bool IsNullCipher; + bool IsNullCipher, IsAeadCipher; const struct evp_cipher_st *Cipher; struct evp_cipher_ctx_st *Ctx; bool Encrypt; @@ -523,6 +525,7 @@ CIPHER *NewCipher(char *name); void FreeCipher(CIPHER *c); void SetCipherKey(CIPHER *c, void *key, bool enc); UINT CipherProcess(CIPHER *c, void *iv, void *dest, void *src, UINT size); +UINT CipherProcessAead(CIPHER *c, void *iv, void *tag, UINT tag_size, void *dest, void *src, UINT src_size, void *aad, UINT aad_size); // Hashing MD *NewMd(char *name); From 9afcc91ae1dd76745ca8218a8c42e7b242aa0500 Mon Sep 17 00:00:00 2001 From: Davide Beatrici Date: Sat, 3 Nov 2018 16:14:56 +0100 Subject: [PATCH 2/3] Cedar/Proto_OpenVPN: add support for GCM ciphers --- src/Cedar/Proto_OpenVPN.c | 310 +++++++++++++++++++++++++------------- src/Cedar/Proto_OpenVPN.h | 4 +- 2 files changed, 207 insertions(+), 107 deletions(-) diff --git a/src/Cedar/Proto_OpenVPN.c b/src/Cedar/Proto_OpenVPN.c index 09a585dc..fd9af585 100644 --- a/src/Cedar/Proto_OpenVPN.c +++ b/src/Cedar/Proto_OpenVPN.c @@ -176,88 +176,131 @@ void OvsLog(OPENVPN_SERVER *s, OPENVPN_SESSION *se, OPENVPN_CHANNEL *c, char *na } // Encrypt the data -UINT OvsEncrypt(CIPHER *cipher, MD *md, UCHAR *iv, UCHAR *dest, UCHAR *src, UINT size) +UINT OvsEncrypt(CIPHER *cipher, MD *md, UCHAR *iv, UCHAR *tag, UCHAR *dest, UCHAR *src, UINT src_size, UCHAR *aad, UINT aad_size) { - UINT dest_size, ret; // Validate arguments - if (cipher == NULL || md == NULL) + if (cipher == NULL || (cipher->IsAeadCipher == false && md == NULL)) { return 0; } - // Encrypt - dest_size = CipherProcess(cipher, iv, dest + md->Size + cipher->IvSize, src, size); - if (dest_size == 0) + if (cipher->IsAeadCipher) { - Debug("OvsEncrypt(): CipherProcess() failed!\n"); - return 0; + // Encrypt in AEAD mode (no HMAC) + UINT dest_size = CipherProcessAead(cipher, iv, tag, 16, dest, src, src_size, aad, aad_size); + if (dest_size == 0) + { + Debug("OvsEncrypt(): CipherProcessAead() failed!\n"); + return 0; + } + + return dest_size; } - - // Copy the IV - Copy(dest + md->Size, iv, cipher->IvSize); - dest_size += cipher->IvSize; - - // Calculate the HMAC - ret = MdProcess(md, dest, dest + md->Size, dest_size); - if (ret == 0) + else { - Debug("OvsEncrypt(): MdProcess() failed!\n"); - return 0; - } + // Encrypt in non-AEAD mode (with HMAC) + UINT ret; + UINT dest_size = CipherProcess(cipher, iv, dest + md->Size + cipher->IvSize, src, src_size); + if (dest_size == 0) + { + Debug("OvsEncrypt(): CipherProcess() failed!\n"); + return 0; + } - return dest_size + ret; + // Copy the IV + Copy(dest + md->Size, iv, cipher->IvSize); + dest_size += cipher->IvSize; + + // Calculate the HMAC + ret = MdProcess(md, dest, dest + md->Size, dest_size); + if (ret == 0) + { + Debug("OvsEncrypt(): MdProcess() failed!\n"); + return 0; + } + + return dest_size + ret; + } } // Decrypt the data -UINT OvsDecrypt(CIPHER *cipher, MD *md, UCHAR *dest, UCHAR *src, UINT size) +UINT OvsDecrypt(CIPHER *cipher, MD *md, UCHAR *iv, UCHAR *dest, UCHAR *src, UINT size) { - UCHAR *hmac; - UCHAR *iv; - UCHAR hmac_test[128]; // Validate arguments - if (cipher == NULL || md == NULL) + if (cipher == NULL) { return 0; } - if (size < (md->Size + cipher->IvSize + sizeof(UINT))) + if (cipher->IsAeadCipher) { - return 0; - } + UCHAR *tag = src; - // HMAC - hmac = src; - src += md->Size; - size -= md->Size; - - if (MdProcess(md, hmac_test, src, size) == 0) - { - Debug("OvsDecrypt(): MdProcess() failed!\n"); - return 0; - } - - if (Cmp(hmac_test, hmac, md->Size) != 0) - { - Debug("OvsDecrypt(): HMAC verification failed!\n"); - return 0; - } - - // IV - iv = src; - src += cipher->IvSize; - size -= cipher->IvSize; - - // Payload - if (size >= 1 && (cipher->BlockSize == 0 || (size % cipher->BlockSize) == 0)) - { - // Decryption - UINT ret = CipherProcess(cipher, iv, dest, src, size); - if (ret == 0) + if (iv == NULL || size <= OPENVPN_TAG_SIZE) { - Debug("OvsDecrypt(): CipherProcess() failed!\n"); + return 0; } - return ret; + src += OPENVPN_TAG_SIZE; + size -= OPENVPN_TAG_SIZE; + + // Payload + if (size >= 1 && (cipher->BlockSize == 0 || (size % cipher->BlockSize) == 0)) + { + // Decryption + UINT ret = CipherProcessAead(cipher, iv, tag, OPENVPN_TAG_SIZE, dest, src, size, iv, sizeof(UINT)); + if (ret == 0) + { + Debug("OvsDecrypt(): CipherProcessAead() failed!\n"); + } + + return ret; + } + } + else + { + UCHAR *hmac; + UCHAR hmac_test[128]; + + if (md == NULL || iv == NULL || size < (md->Size + cipher->IvSize + sizeof(UINT))) + { + return 0; + } + + // HMAC + hmac = src; + src += md->Size; + size -= md->Size; + + if (MdProcess(md, hmac_test, src, size) == 0) + { + Debug("OvsDecrypt(): MdProcess() failed!\n"); + return 0; + } + + if (Cmp(hmac_test, hmac, md->Size) != 0) + { + Debug("OvsDecrypt(): HMAC verification failed!\n"); + return 0; + } + + // IV + Copy(iv, src, cipher->IvSize); + src += cipher->IvSize; + size -= cipher->IvSize; + + // Payload + if (size >= 1 && (cipher->BlockSize == 0 || (size % cipher->BlockSize) == 0)) + { + // Decryption + UINT ret = CipherProcess(cipher, iv, dest, src, size); + if (ret == 0) + { + Debug("OvsDecrypt(): CipherProcess() failed!\n"); + } + + return ret; + } } return 0; @@ -373,32 +416,42 @@ void OvsProceccRecvPacket(OPENVPN_SERVER *s, UDPPACKET *p, UINT protocol) OPENVPN_CHANNEL *c = se->Channels[recv_packet->KeyId]; if (c->Status == OPENVPN_CHANNEL_STATUS_ESTABLISHED) { - UINT size = OvsDecrypt(c->CipherDecrypt, c->MdRecv, s->TmpBuf, recv_packet->Data, recv_packet->DataSize); - if (size >= sizeof(UINT)) + UINT size; + UCHAR *data = s->TmpBuf; + if (c->CipherDecrypt->IsAeadCipher) { - UCHAR *data = s->TmpBuf; + // Update variable part (packet ID) of IV + Copy(c->IvRecv, recv_packet->Data, sizeof(recv_packet->PacketId)); - // Update of last communication time - se->LastCommTick = s->Now; + // Decrypt + size = OvsDecrypt(c->CipherDecrypt, NULL, c->IvRecv, data, recv_packet->Data + sizeof(UINT), recv_packet->DataSize - sizeof(UINT)); + } + else + { + // Decrypt + size = OvsDecrypt(c->CipherDecrypt, c->MdRecv, c->IvRecv, data, recv_packet->Data, recv_packet->DataSize); // Seek buffer after the packet ID data += sizeof(UINT); size -= sizeof(UINT); + } - if (size < sizeof(ping_signature) || Cmp(data, ping_signature, sizeof(ping_signature)) != 0) + // Update of last communication time + se->LastCommTick = s->Now; + + if (size < sizeof(ping_signature) || Cmp(data, ping_signature, sizeof(ping_signature)) != 0) + { + // Receive a packet! + if (se->Ipc != NULL) { - // Receive a packet! - if (se->Ipc != NULL) + switch (se->Mode) { - switch (se->Mode) - { - case OPENVPN_MODE_L2: // Send an Ethernet packet to a session - IPCSendL2(se->Ipc, data, size); - break; - case OPENVPN_MODE_L3: // Send an IPv4 packet to a session - IPCSendIPv4(se->Ipc, data, size); - break; - } + case OPENVPN_MODE_L2: // Send an Ethernet packet to a session + IPCSendL2(se->Ipc, data, size); + break; + case OPENVPN_MODE_L3: // Send an IPv4 packet to a session + IPCSendIPv4(se->Ipc, data, size); + break; } } } @@ -818,7 +871,7 @@ void OvsSetupSessionParameters(OPENVPN_SERVER *s, OPENVPN_SESSION *se, OPENVPN_C LIST *o; BUF *b; char opt_str[MAX_SIZE]; - char *cipher_name; + char *cipher_name, *md_name; // Validate arguments if (s == NULL || se == NULL || c == NULL || data == NULL) { @@ -897,7 +950,6 @@ void OvsSetupSessionParameters(OPENVPN_SERVER *s, OPENVPN_SESSION *se, OPENVPN_C if (se->Protocol == OPENVPN_PROTOCOL_TCP) { // TCP - // UDP if (IsIP6(&se->ClientIp) == false) { StrCpy(c->Proto, sizeof(c->Proto), "TCPv4_SERVER"); @@ -922,12 +974,9 @@ void OvsSetupSessionParameters(OPENVPN_SERVER *s, OPENVPN_SESSION *se, OPENVPN_C // Encryption algorithm cipher_name = EntryListStrValue(o, "cipher"); - c->CipherEncrypt = OvsGetCipher(cipher_name); - c->CipherDecrypt = OvsGetCipher(cipher_name); // Hash algorithm - c->MdSend = OvsGetMd(EntryListStrValue(o, "auth")); - c->MdRecv = NewMd(c->MdSend->Name); + md_name = EntryListStrValue(o, "auth"); // Random number generation Rand(c->ServerKey.Random1, sizeof(c->ServerKey.Random1)); @@ -954,13 +1003,26 @@ void OvsSetupSessionParameters(OPENVPN_SERVER *s, OPENVPN_SESSION *se, OPENVPN_C c->ExpansionKey, sizeof(c->ExpansionKey)); FreeBuf(b); - // Set the key + // Set up the encryption algorithm + c->CipherEncrypt = OvsGetCipher(cipher_name); + c->CipherDecrypt = OvsGetCipher(cipher_name); SetCipherKey(c->CipherDecrypt, c->ExpansionKey + 0, false); SetCipherKey(c->CipherEncrypt, c->ExpansionKey + 128, true); - SetMdKey(c->MdRecv, c->ExpansionKey + 64, c->MdRecv->Size); - SetMdKey(c->MdSend, c->ExpansionKey + 192, c->MdSend->Size); - FreeEntryList(o); + if (c->CipherDecrypt->IsAeadCipher) + { + // In AEAD mode the IV is composed by the packet ID and a part of the HMAC key + Copy(c->IvRecv + sizeof(c->LastDataPacketId), c->ExpansionKey + 64, c->CipherDecrypt->IvSize - sizeof(c->LastDataPacketId)); + Copy(c->IvSend + sizeof(c->LastDataPacketId), c->ExpansionKey + 192, c->CipherEncrypt->IvSize - sizeof(c->LastDataPacketId)); + } + else + { + // Set up the hash algorithm + c->MdSend = OvsGetMd(md_name); + c->MdRecv = OvsGetMd(md_name); + SetMdKey(c->MdRecv, c->ExpansionKey + 64, c->MdRecv->Size); + SetMdKey(c->MdSend, c->ExpansionKey + 192, c->MdSend->Size); + } // We pass the cipher name sent from the OpenVPN client, unless it's a different cipher, to prevent a message such as: // WARNING: 'cipher' is used inconsistently, local='cipher AES-128-GCM', remote='cipher aes-128-gcm' @@ -979,9 +1041,11 @@ void OvsSetupSessionParameters(OPENVPN_SERVER *s, OPENVPN_SESSION *se, OPENVPN_C se->LinkMtu, se->TunMtu, c->Proto, - cipher_name, c->MdSend->Name, c->CipherEncrypt->KeySize * 8); - Debug("Building OptionStr: %s\n", c->ServerKey.OptionString); + cipher_name, md_name, c->CipherEncrypt->KeySize * 8); + FreeEntryList(o); + + Debug("OvsSetupSessionParameters(): Built OptionString: %s\n", c->ServerKey.OptionString); OvsLog(s, se, c, "LO_OPTION_STR_SEND", c->ServerKey.OptionString); } @@ -1379,7 +1443,8 @@ OPENVPN_CHANNEL *OvsNewChannel(OPENVPN_SESSION *se, UCHAR key_id) c->KeyId = key_id; - Rand(c->NextIv, sizeof(c->NextIv)); + Rand(c->IvSend, sizeof(c->IvSend)); + Rand(c->IvRecv, sizeof(c->IvRecv)); //c->NextRekey = se->Server->Now + (UINT64)5000; @@ -1427,8 +1492,7 @@ UINT64 OvsNewServerSessionId(OPENVPN_SERVER *s) // Build and submit the OpenVPN data packet void OvsSendDataPacket(OPENVPN_CHANNEL *c, UCHAR key_id, UINT data_packet_id, void *data, UINT data_size) { - UCHAR *encrypted_data; - UINT encrypted_size; + const UCHAR op = ((OPENVPN_P_DATA_V1 << 3) & 0xF8) | (key_id & 0x07); UCHAR *dest_data; UINT dest_size; // Validate arguments @@ -1437,29 +1501,63 @@ void OvsSendDataPacket(OPENVPN_CHANNEL *c, UCHAR key_id, UINT data_packet_id, vo return; } - // Generate the data to be encrypted - encrypted_size = sizeof(UINT) + data_size; - encrypted_data = ZeroMalloc(encrypted_size); + // [ xxx ] = unprotected + // [ - xxx - ] = authenticated + // [ * xxx * ] = encrypted and authenticated - WRITE_UINT(encrypted_data, data_packet_id); - Copy(encrypted_data + sizeof(UINT), data, data_size); + if (c->CipherEncrypt->IsAeadCipher) + { + // [ opcode ] [ - packet ID - ] [ TAG ] [ * packet payload * ] + UCHAR tag[16]; - // Prepare a buffer to store the results - dest_data = Malloc(sizeof(UCHAR) + c->MdSend->Size + c->CipherEncrypt->IvSize + encrypted_size + 256); + // Update variable part (packet ID) of IV + WRITE_UINT(c->IvSend, data_packet_id); - // Encrypt - dest_size = OvsEncrypt(c->CipherEncrypt, c->MdSend, c->NextIv, dest_data + sizeof(CHAR), encrypted_data, encrypted_size); - dest_size += sizeof(UCHAR); + // Prepare a buffer to store the results + dest_data = Malloc(sizeof(op) + sizeof(data_packet_id) + sizeof(tag) + data_size + 256); - // Update the NextIV - Copy(c->NextIv, dest_data + dest_size - c->CipherEncrypt->IvSize, c->CipherEncrypt->IvSize); + // Set data size to the maximum known + dest_size = sizeof(op) + sizeof(data_packet_id) + sizeof(tag); - // Op-code - dest_data[0] = ((OPENVPN_P_DATA_V1 << 3) & 0xF8) | (key_id & 0x07); + // Write opcode + dest_data[0] = op; + + // Write packet ID + WRITE_UINT(dest_data + sizeof(op), data_packet_id); + + // Write encrypted payload + dest_size += OvsEncrypt(c->CipherEncrypt, NULL, c->IvSend, tag, dest_data + dest_size, data, data_size, c->IvSend, sizeof(data_packet_id)); + + // Write authentication tag + Copy(dest_data + sizeof(op) + sizeof(data_packet_id), tag, sizeof(tag)); + } + else + { + // [ opcode ] [ HMAC ] [ - IV - ] [ * packet ID * ] [ * packet payload * ] + UINT encrypted_size = sizeof(data_packet_id) + data_size; + UCHAR *encrypted_data = ZeroMalloc(encrypted_size); + WRITE_UINT(encrypted_data, data_packet_id); + Copy(encrypted_data + sizeof(data_packet_id), data, data_size); + + // Prepare a buffer to store the results + dest_data = Malloc(sizeof(op) + c->MdSend->Size + c->CipherEncrypt->IvSize + encrypted_size + 256); + + // Set data size to the maximum known + dest_size = sizeof(op); + + // Write opcode + dest_data[0] = op; + + // Write IV, encrypted packet ID and payload + dest_size += OvsEncrypt(c->CipherEncrypt, c->MdSend, c->IvSend, NULL, dest_data + sizeof(op), encrypted_data, encrypted_size, NULL, 0); + + Free(encrypted_data); + + // Update the IV + Copy(c->IvSend, dest_data + dest_size - c->CipherEncrypt->IvSize, c->CipherEncrypt->IvSize); + } OvsSendPacketRawNow(c->Server, c->Session, dest_data, dest_size); - - Free(encrypted_data); } // Build an OpenVPN control packet diff --git a/src/Cedar/Proto_OpenVPN.h b/src/Cedar/Proto_OpenVPN.h index 0415b44d..2116a936 100644 --- a/src/Cedar/Proto_OpenVPN.h +++ b/src/Cedar/Proto_OpenVPN.h @@ -127,6 +127,7 @@ #define OPENVPN_MAX_SSL_RECV_BUF_SIZE (256 * 1024) // SSL receive buffer maximum length #define OPENVPN_MAX_KEY_SIZE 64 // Maximum key size +#define OPENVPN_TAG_SIZE 16 // Tag size (for packet authentication in AEAD mode) #define OPENVPN_TMP_BUFFER_SIZE (65536 + 256) // Temporary buffer size @@ -241,9 +242,10 @@ struct OPENVPN_CHANNEL CIPHER *CipherDecrypt; // Decryption algorithm MD *MdSend; // Transmission MD algorithm MD *MdRecv; // Reception MD algorithm + UCHAR IvSend[64]; // Transmission IV + UCHAR IvRecv[64]; // Reception IV UCHAR MasterSecret[48]; // Master Secret UCHAR ExpansionKey[256]; // Expansion Key - UCHAR NextIv[64]; // Next IV UINT LastDataPacketId; // Previous Data Packet ID UINT64 EstablishedTick; // Established time UCHAR KeyId; // KEY ID From 0357024e62177e9bf8577ff15205314b93d4762c Mon Sep 17 00:00:00 2001 From: Davide Beatrici Date: Sat, 3 Nov 2018 16:44:50 +0100 Subject: [PATCH 3/3] hamcore/openvpn_sample.ovpn: improve "cipher" and "auth" documentation, remove list of supported ciphers --- src/bin/hamcore/openvpn_sample.ovpn | 11 +++-------- 1 file changed, 3 insertions(+), 8 deletions(-) diff --git a/src/bin/hamcore/openvpn_sample.ovpn b/src/bin/hamcore/openvpn_sample.ovpn index 3b7c3868..ec3e5e63 100644 --- a/src/bin/hamcore/openvpn_sample.ovpn +++ b/src/bin/hamcore/openvpn_sample.ovpn @@ -98,14 +98,9 @@ $TAG_BEFORE_REMOTE$remote $TAG_HOSTNAME$ $TAG_PORT$ ############################################################################### # The encryption and authentication algorithm. # -# Default setting is good. Modify it as you prefer. -# When you specify an unsupported algorithm, the error will occur. -# -# The supported algorithms are as follows: -# cipher: [NULL-CIPHER] NULL AES-128-CBC AES-192-CBC AES-256-CBC BF-CBC -# CAST-CBC CAST5-CBC DES-CBC DES-EDE-CBC DES-EDE3-CBC DESX-CBC -# RC2-40-CBC RC2-64-CBC RC2-CBC CAMELLIA-128-CBC CAMELLIA-192-CBC CAMELLIA-256-CBC -# auth: SHA SHA1 SHA256 SHA384 SHA512 MD5 MD4 RMD160 +# The default setting is compatible with most clients. Modify it as you prefer. +# It is recommended to use a better algorithm if your client supports it. +# When you specify an unsupported algorithm, an error will occur. cipher AES-128-CBC auth SHA1