7 " ˆl–ß=¿Jõ7µ4 …p@¸ÓÊbÑ¿È ƒq–YÀƽ [Note: This file has not been updated for OpenSSH versions after OpenSSH-1.2 and should be considered OBSOLETE. It has been left in the distribution because some of its information may still be useful to developers.] This document is intended for those who wish to read the ssh source code. This tries to give an overview of the structure of the code. Copyright (c) 1995 Tatu Ylonen Updated 17 Nov 1995. Updated 19 Oct 1999 for OpenSSH-1.2 Updated 20 May 2001 note obsolete for > OpenSSH-1.2 The software consists of ssh (client), sshd (server), scp, sdist, and the auxiliary programs ssh-keygen, ssh-agent, ssh-add, and make-ssh-known-hosts. The main program for each of these is in a .c file with the same name. There are some subsystems/abstractions that are used by a number of these programs. Buffer manipulation routines - These provide an arbitrary size buffer, where data can be appended. Data can be consumed from either end. The code is used heavily throughout ssh. The buffer manipulation functions are in sshbuf*.c (header sshbuf.h). Compression Library - Ssh uses the GNU GZIP compression library (ZLIB). Encryption/Decryption - Ssh contains several encryption algorithms. These are all accessed through the cipher.h interface. The interface code is in cipher.c, and the implementations are either in libc or LibreSSL. Multiple Precision Integer Library - Uses the LibreSSL BIGNUM sublibrary. Random Numbers - Uses arc4random() and such. RSA key generation, encryption, decryption - Ssh uses the RSA routines in libssl. RSA key files - RSA keys are stored in files with a special format. The code to read/write these files is in authfile.c. The files are normally encrypted with a passphrase. The functions to read passphrases are in readpass.c (the same code is used to read passwords). Binary packet protocol - The ssh binary packet protocol is implemented in packet.c. The code in packet.c does not concern itself with packet types or their execution; it contains code to build packets, to receive them and extract data from them, and the code to compress and/or encrypt packets. - The code in packet.c calls the buffer manipulation routines (buffer.c, bufaux.c), compression routines (zlib), and the encryption routines. X11, TCP/IP, and Agent forwarding - Code for various types of channel forwarding is in channels.c. The file defines a generic framework for arbitrary communication channels inside the secure channel, and uses this framework to implement X11 forwarding, TCP/IP forwarding, and authentication agent forwarding. The new, Protocol 1.5, channel close implementation is in nchan.c Authentication agent - Code to communicate with the authentication agent is in authfd.c. Authentication methods - Code for various authentication methods resides in auth-*.c (auth-passwd.c, auth-rh-rsa.c, auth-rhosts.c, auth-rsa.c). This code is linked into the server. The routines also manipulate known hosts files using code in hostfile.c. Code in canohost.c is used to retrieve the canonical host name of the remote host. Code in match.c is used to match host names. - In the client end, authentication code is in sshconnect.c. It reads Passwords/passphrases using code in readpass.c. It reads RSA key files with authfile.c. It communicates the authentication agent using authfd.c. The ssh client - The client main program is in ssh.c. It first parses arguments and reads configuration (readconf.c), then calls ssh_connect (in sshconnect.c) to open a connection to the server (possibly via a proxy), and performs authentication (ssh_login in sshconnect.c). It then makes any pty, forwarding, etc. requests. It may call code in ttymodes.c to encode current tty modes. Finally it