Annotation of src/usr.bin/ssh/OVERVIEW, Revision 1.14
1.6 stevesk 1: [Note: This file has not been updated for OpenSSH versions after
2: OpenSSH-1.2 and should be considered OBSOLETE. It has been left in
3: the distribution because some of its information may still be useful
4: to developers.]
5:
1.5 deraadt 6: This document is intended for those who wish to read the ssh source
1.1 deraadt 7: code. This tries to give an overview of the structure of the code.
1.7 djm 8:
1.1 deraadt 9: Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>
10: Updated 17 Nov 1995.
1.3 markus 11: Updated 19 Oct 1999 for OpenSSH-1.2
1.6 stevesk 12: Updated 20 May 2001 note obsolete for > OpenSSH-1.2
1.1 deraadt 13:
14: The software consists of ssh (client), sshd (server), scp, sdist, and
15: the auxiliary programs ssh-keygen, ssh-agent, ssh-add, and
16: make-ssh-known-hosts. The main program for each of these is in a .c
17: file with the same name.
18:
19: There are some subsystems/abstractions that are used by a number of
20: these programs.
21:
22: Buffer manipulation routines
1.7 djm 23:
1.1 deraadt 24: - These provide an arbitrary size buffer, where data can be appended.
25: Data can be consumed from either end. The code is used heavily
1.13 djm 26: throughout ssh. The buffer manipulation functions are in
27: sshbuf*.c (header sshbuf.h).
1.1 deraadt 28:
29: Compression Library
1.7 djm 30:
1.4 deraadt 31: - Ssh uses the GNU GZIP compression library (ZLIB).
1.1 deraadt 32:
33: Encryption/Decryption
34:
35: - Ssh contains several encryption algorithms. These are all
36: accessed through the cipher.h interface. The interface code is
1.4 deraadt 37: in cipher.c, and the implementations are in libc.
1.1 deraadt 38:
39: Multiple Precision Integer Library
40:
1.2 deraadt 41: - Uses the SSLeay BIGNUM sublibrary.
1.1 deraadt 42:
43: Random Numbers
44:
1.2 deraadt 45: - Uses arc4random() and such.
1.1 deraadt 46:
47: RSA key generation, encryption, decryption
48:
1.2 deraadt 49: - Ssh uses the RSA routines in libssl.
1.1 deraadt 50:
51: RSA key files
52:
53: - RSA keys are stored in files with a special format. The code to
54: read/write these files is in authfile.c. The files are normally
55: encrypted with a passphrase. The functions to read passphrases
56: are in readpass.c (the same code is used to read passwords).
57:
58: Binary packet protocol
59:
60: - The ssh binary packet protocol is implemented in packet.c. The
61: code in packet.c does not concern itself with packet types or their
62: execution; it contains code to build packets, to receive them and
63: extract data from them, and the code to compress and/or encrypt
1.14 ! dtucker 64: packets.
1.1 deraadt 65:
66: - The code in packet.c calls the buffer manipulation routines
1.12 markus 67: (buffer.c, bufaux.c), compression routines (zlib), and the
68: encryption routines.
1.1 deraadt 69:
70: X11, TCP/IP, and Agent forwarding
71:
72: - Code for various types of channel forwarding is in channels.c.
73: The file defines a generic framework for arbitrary communication
74: channels inside the secure channel, and uses this framework to
75: implement X11 forwarding, TCP/IP forwarding, and authentication
76: agent forwarding.
1.3 markus 77: The new, Protocol 1.5, channel close implementation is in nchan.c
1.1 deraadt 78:
79: Authentication agent
80:
1.3 markus 81: - Code to communicate with the authentication agent is in authfd.c.
1.1 deraadt 82:
83: Authentication methods
84:
85: - Code for various authentication methods resides in auth-*.c
86: (auth-passwd.c, auth-rh-rsa.c, auth-rhosts.c, auth-rsa.c). This
87: code is linked into the server. The routines also manipulate
88: known hosts files using code in hostfile.c. Code in canohost.c
89: is used to retrieve the canonical host name of the remote host.
1.7 djm 90: Code in match.c is used to match host names.
1.1 deraadt 91:
92: - In the client end, authentication code is in sshconnect.c. It
93: reads Passwords/passphrases using code in readpass.c. It reads
94: RSA key files with authfile.c. It communicates the
95: authentication agent using authfd.c.
96:
97: The ssh client
98:
99: - The client main program is in ssh.c. It first parses arguments
100: and reads configuration (readconf.c), then calls ssh_connect (in
101: sshconnect.c) to open a connection to the server (possibly via a
102: proxy), and performs authentication (ssh_login in sshconnect.c).
103: It then makes any pty, forwarding, etc. requests. It may call
104: code in ttymodes.c to encode current tty modes. Finally it
105: calls client_loop in clientloop.c. This does the real work for
106: the session.
107:
108: Pseudo-tty manipulation and tty modes
109:
110: - Code to allocate and use a pseudo tty is in pty.c. Code to
111: encode and set terminal modes is in ttymodes.c.
112:
113: Logging in (updating utmp, lastlog, etc.)
114:
115: - The code to do things that are done when a user logs in are in
116: login.c. This includes things such as updating the utmp, wtmp,
117: and lastlog files. Some of the code is in sshd.c.
118:
119: Writing to the system log and terminal
120:
121: - The programs use the functions fatal(), log(), debug(), error()
122: in many places to write messages to system log or user's
123: terminal. The implementation that logs to system log is in
124: log-server.c; it is used in the server program. The other
125: programs use an implementation that sends output to stderr; it
126: is in log-client.c. The definitions are in ssh.h.
127:
128: The sshd server (daemon)
129:
130: - The sshd daemon starts by processing arguments and reading the
131: configuration file (servconf.c). It then reads the host key,
132: starts listening for connections, and generates the server key.
133: The server key will be regenerated every hour by an alarm.
134:
135: - When the server receives a connection, it forks, disables the
136: regeneration alarm, and starts communicating with the client.
137: They first perform identification string exchange, then
138: negotiate encryption, then perform authentication, preparatory
139: operations, and finally the server enters the normal session
140: mode by calling server_loop in serverloop.c. This does the real
141: work, calling functions in other modules.
1.7 djm 142:
1.1 deraadt 143: - The code for the server is in sshd.c. It contains a lot of
144: stuff, including:
1.7 djm 145: - server main program
1.1 deraadt 146: - waiting for connections
147: - processing new connection
148: - authentication
149: - preparatory operations
150: - building up the execution environment for the user program
151: - starting the user program.
152:
153: Auxiliary files
154:
155: - There are several other files in the distribution that contain
156: various auxiliary routines:
1.7 djm 157: ssh.h the main header file for ssh (various definitions)
1.1 deraadt 158: uidswap.c uid-swapping
159: xmalloc.c "safe" malloc routines
1.10 djm 160:
1.14 ! dtucker 161: $OpenBSD: OVERVIEW,v 1.13 2018/07/10 06:45:29 djm Exp $
![[BACK]](/icons/back.gif){kind=icon}
Return to OVERVIEW CVS log ![[TXT]](/icons/text.gif){kind=icon}
![[DIR]](/icons/dir.gif){kind=icon}
Up to [local] / src / usr.bin / ssh