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Diffstat (limited to 'Documentation/networking/tls.txt')
| -rw-r--r-- | Documentation/networking/tls.txt | 197 |
1 files changed, 0 insertions, 197 deletions
diff --git a/Documentation/networking/tls.txt b/Documentation/networking/tls.txt deleted file mode 100644 index 58b5ef75f1b7..000000000000 --- a/Documentation/networking/tls.txt +++ /dev/null @@ -1,197 +0,0 @@ -Overview -======== - -Transport Layer Security (TLS) is a Upper Layer Protocol (ULP) that runs over -TCP. TLS provides end-to-end data integrity and confidentiality. - -User interface -============== - -Creating a TLS connection -------------------------- - -First create a new TCP socket and set the TLS ULP. - - sock = socket(AF_INET, SOCK_STREAM, 0); - setsockopt(sock, SOL_TCP, TCP_ULP, "tls", sizeof("tls")); - -Setting the TLS ULP allows us to set/get TLS socket options. Currently -only the symmetric encryption is handled in the kernel. After the TLS -handshake is complete, we have all the parameters required to move the -data-path to the kernel. There is a separate socket option for moving -the transmit and the receive into the kernel. - - /* From linux/tls.h */ - struct tls_crypto_info { - unsigned short version; - unsigned short cipher_type; - }; - - struct tls12_crypto_info_aes_gcm_128 { - struct tls_crypto_info info; - unsigned char iv[TLS_CIPHER_AES_GCM_128_IV_SIZE]; - unsigned char key[TLS_CIPHER_AES_GCM_128_KEY_SIZE]; - unsigned char salt[TLS_CIPHER_AES_GCM_128_SALT_SIZE]; - unsigned char rec_seq[TLS_CIPHER_AES_GCM_128_REC_SEQ_SIZE]; - }; - - - struct tls12_crypto_info_aes_gcm_128 crypto_info; - - crypto_info.info.version = TLS_1_2_VERSION; - crypto_info.info.cipher_type = TLS_CIPHER_AES_GCM_128; - memcpy(crypto_info.iv, iv_write, TLS_CIPHER_AES_GCM_128_IV_SIZE); - memcpy(crypto_info.rec_seq, seq_number_write, - TLS_CIPHER_AES_GCM_128_REC_SEQ_SIZE); - memcpy(crypto_info.key, cipher_key_write, TLS_CIPHER_AES_GCM_128_KEY_SIZE); - memcpy(crypto_info.salt, implicit_iv_write, TLS_CIPHER_AES_GCM_128_SALT_SIZE); - - setsockopt(sock, SOL_TLS, TLS_TX, &crypto_info, sizeof(crypto_info)); - -Transmit and receive are set separately, but the setup is the same, using either -TLS_TX or TLS_RX. - -Sending TLS application data ----------------------------- - -After setting the TLS_TX socket option all application data sent over this -socket is encrypted using TLS and the parameters provided in the socket option. -For example, we can send an encrypted hello world record as follows: - - const char *msg = "hello world\n"; - send(sock, msg, strlen(msg)); - -send() data is directly encrypted from the userspace buffer provided -to the encrypted kernel send buffer if possible. - -The sendfile system call will send the file's data over TLS records of maximum -length (2^14). - - file = open(filename, O_RDONLY); - fstat(file, &stat); - sendfile(sock, file, &offset, stat.st_size); - -TLS records are created and sent after each send() call, unless -MSG_MORE is passed. MSG_MORE will delay creation of a record until -MSG_MORE is not passed, or the maximum record size is reached. - -The kernel will need to allocate a buffer for the encrypted data. -This buffer is allocated at the time send() is called, such that -either the entire send() call will return -ENOMEM (or block waiting -for memory), or the encryption will always succeed. If send() returns --ENOMEM and some data was left on the socket buffer from a previous -call using MSG_MORE, the MSG_MORE data is left on the socket buffer. - -Receiving TLS application data ------------------------------- - -After setting the TLS_RX socket option, all recv family socket calls -are decrypted using TLS parameters provided. A full TLS record must -be received before decryption can happen. - - char buffer[16384]; - recv(sock, buffer, 16384); - -Received data is decrypted directly in to the user buffer if it is -large enough, and no additional allocations occur. If the userspace -buffer is too small, data is decrypted in the kernel and copied to -userspace. - -EINVAL is returned if the TLS version in the received message does not -match the version passed in setsockopt. - -EMSGSIZE is returned if the received message is too big. - -EBADMSG is returned if decryption failed for any other reason. - -Send TLS control messages -------------------------- - -Other than application data, TLS has control messages such as alert -messages (record type 21) and handshake messages (record type 22), etc. -These messages can be sent over the socket by providing the TLS record type -via a CMSG. For example the following function sends @data of @length bytes -using a record of type @record_type. - -/* send TLS control message using record_type */ - static int klts_send_ctrl_message(int sock, unsigned char record_type, - void *data, size_t length) - { - struct msghdr msg = {0}; - int cmsg_len = sizeof(record_type); - struct cmsghdr *cmsg; - char buf[CMSG_SPACE(cmsg_len)]; - struct iovec msg_iov; /* Vector of data to send/receive into. */ - - msg.msg_control = buf; - msg.msg_controllen = sizeof(buf); - cmsg = CMSG_FIRSTHDR(&msg); - cmsg->cmsg_level = SOL_TLS; - cmsg->cmsg_type = TLS_SET_RECORD_TYPE; - cmsg->cmsg_len = CMSG_LEN(cmsg_len); - *CMSG_DATA(cmsg) = record_type; - msg.msg_controllen = cmsg->cmsg_len; - - msg_iov.iov_base = data; - msg_iov.iov_len = length; - msg.msg_iov = &msg_iov; - msg.msg_iovlen = 1; - - return sendmsg(sock, &msg, 0); - } - -Control message data should be provided unencrypted, and will be -encrypted by the kernel. - -Receiving TLS control messages ------------------------------- - -TLS control messages are passed in the userspace buffer, with message -type passed via cmsg. If no cmsg buffer is provided, an error is -returned if a control message is received. Data messages may be -received without a cmsg buffer set. - - char buffer[16384]; - char cmsg[CMSG_SPACE(sizeof(unsigned char))]; - struct msghdr msg = {0}; - msg.msg_control = cmsg; - msg.msg_controllen = sizeof(cmsg); - - struct iovec msg_iov; - msg_iov.iov_base = buffer; - msg_iov.iov_len = 16384; - - msg.msg_iov = &msg_iov; - msg.msg_iovlen = 1; - - int ret = recvmsg(sock, &msg, 0 /* flags */); - - struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg); - if (cmsg->cmsg_level == SOL_TLS && - cmsg->cmsg_type == TLS_GET_RECORD_TYPE) { - int record_type = *((unsigned char *)CMSG_DATA(cmsg)); - // Do something with record_type, and control message data in - // buffer. - // - // Note that record_type may be == to application data (23). - } else { - // Buffer contains application data. - } - -recv will never return data from mixed types of TLS records. - -Integrating in to userspace TLS library ---------------------------------------- - -At a high level, the kernel TLS ULP is a replacement for the record -layer of a userspace TLS library. - -A patchset to OpenSSL to use ktls as the record layer is here: - -https://github.com/Mellanox/openssl/commits/tls_rx2 - -An example of calling send directly after a handshake using -gnutls. Since it doesn't implement a full record layer, control -messages are not supported: - -https://github.com/ktls/af_ktls-tool/commits/RX |