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Diffstat (limited to 'crypto/openssh/OVERVIEW')
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diff --git a/crypto/openssh/OVERVIEW b/crypto/openssh/OVERVIEW deleted file mode 100644 index 2e1cc0b..0000000 --- a/crypto/openssh/OVERVIEW +++ /dev/null @@ -1,168 +0,0 @@ -[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 <ylo@cs.hut.fi> -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 basic buffer manipulation functions are in - buffer.c (header buffer.h), and additional code to manipulate specific - data types is in bufaux.c. - - 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 in libc. - - Multiple Precision Integer Library - - - Uses the SSLeay 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. CRC code comes from crc32.c. - - - The code in packet.c calls the buffer manipulation routines - (buffer.c, bufaux.c), compression routines (compress.c, 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 - calls client_loop in clientloop.c. This does the real work for - the session. - - - The client is suid root. It tries to temporarily give up this - rights while reading the configuration data. The root - privileges are only used to make the connection (from a - privileged socket). Any extra privileges are dropped before - calling ssh_login. - - Pseudo-tty manipulation and tty modes - - - Code to allocate and use a pseudo tty is in pty.c. Code to - encode and set terminal modes is in ttymodes.c. - - Logging in (updating utmp, lastlog, etc.) - - - The code to do things that are done when a user logs in are in - login.c. This includes things such as updating the utmp, wtmp, - and lastlog files. Some of the code is in sshd.c. - - Writing to the system log and terminal - - - The programs use the functions fatal(), log(), debug(), error() - in many places to write messages to system log or user's - terminal. The implementation that logs to system log is in - log-server.c; it is used in the server program. The other - programs use an implementation that sends output to stderr; it - is in log-client.c. The definitions are in ssh.h. - - The sshd server (daemon) - - - The sshd daemon starts by processing arguments and reading the - configuration file (servconf.c). It then reads the host key, - starts listening for connections, and generates the server key. - The server key will be regenerated every hour by an alarm. - - - When the server receives a connection, it forks, disables the - regeneration alarm, and starts communicating with the client. - They first perform identification string exchange, then - negotiate encryption, then perform authentication, preparatory - operations, and finally the server enters the normal session - mode by calling server_loop in serverloop.c. This does the real - work, calling functions in other modules. - - - The code for the server is in sshd.c. It contains a lot of - stuff, including: - - server main program - - waiting for connections - - processing new connection - - authentication - - preparatory operations - - building up the execution environment for the user program - - starting the user program. - - Auxiliary files - - - There are several other files in the distribution that contain - various auxiliary routines: - ssh.h the main header file for ssh (various definitions) - uidswap.c uid-swapping - xmalloc.c "safe" malloc routines - -$OpenBSD: OVERVIEW,v 1.11 2006/08/03 03:34:41 deraadt Exp $ |
