Device and Network Interfaces forgeries(7) NNNNAAAAMMMMEEEE forgeries - how easy it is to forge mail SSSSUUUUMMMMMMMMAAAARRRRYYYY An electronic mail message can easily be forged. Almost everything in it, including the return address, is com- pletely under the control of the sender. An electronic mail message can be manually traced to its origin if (1) all system administrators of intermediate machines are both cooperative and competent, (2) the sender did not break low-level TCP/IP security, and (3) all inter- mediate machines are secure. Users of _c_r_y_p_t_o_g_r_a_p_h_y can automatically ensure the integrity and secrecy of their mail messages, as long as the sending and receiving machines are secure. FFFFOOOORRRRGGGGEEEERRRRIIIIEEEESSSS Like postal mail, electronic mail can be created entirely at the whim of the sender. FFFFrrrroooommmm, SSSSeeeennnnddddeeeerrrr, RRRReeeettttuuuurrrrnnnn----PPPPaaaatttthhhh, and MMMMeeeessssssssaaaaggggeeee----IIIIDDDD can all contain whatever information the sender wants. For example, if you inject a message through sssseeeennnnddddmmmmaaaaiiiillll or qqqqmmmmaaaaiiiillll----iiiinnnnjjjjeeeecccctttt or SSSSMMMMTTTTPPPP, you can simply type in a FFFFrrrroooommmm field. In fact, qqqqmmmmaaaaiiiillll----iiiinnnnjjjjeeeecccctttt lets you set up MMMMAAAAIIIILLLLUUUUSSSSEEEERRRR, MMMMAAAAIIIILLLLHHHHOOOOSSSSTTTT, and MMMMAAAAIIIILLLLNNNNAAAAMMMMEEEE environment variables to produce your desired FFFFrrrroooommmm field on every message. TTTTRRRRAAAACCCCIIIINNNNGGGG FFFFOOOORRRRGGGGEEEERRRRIIIIEEEESSSS Like postal mail, electronic mail is postmarked when it is sent. Each machine that receives an electronic mail message adds a RRRReeeecccceeeeiiiivvvveeeedddd line to the top. A modern RRRReeeecccceeeeiiiivvvveeeedddd line contains quite a bit of information. In conjunction with the machine's logs, it lets a competent system administrator determine where the machine received the message from, as long as the sender did not break low- level TCP/IP security or security on that machine. Large multi-user machines often come with inadequate logging software. Fortunately, a system administrator can easily obtain a copy of a 931/1413/Ident/TAP server, such as ppppiiiiddddeeeennnnttttdddd. Unfortunately, some system administrators fail to do this, and are thus unable to figure out which local user was responsible for generating a message. If all intermediate system administrators are competent, and the sender did not break machine security or low-level TCP/IP security, it is possible to trace a message back- wards. Unfortunately, some traces are stymied by SunOS 5.11 Last change: 1 Device and Network Interfaces forgeries(7) intermediate system administrators who are uncooperative or untrustworthy. CCCCRRRRYYYYPPPPTTTTOOOOGGGGRRRRAAAAPPPPHHHHYYYY The sender of a mail message may place his message into a _c_r_y_p_t_o_g_r_a_p_h_i_c envelope stamped with his seal. Strong cryp- tography guarantees that any two messages with the same seal were sent by the same cryptographic entity: perhaps a sin- gle person, perhaps a group of cooperating people, but in any case somebody who knows a secret originally held only by the creator of the seal. The seal is called a _p_u_b_l_i_c _k_e_y. Unfortunately, the creator of the seal is often an insecure machine, or an untrustworthy central agency, but most of the time seals are kept secure. One popular cryptographic program is ppppggggpppp. SSSSEEEEEEEE AAAALLLLSSSSOOOO pgp(1), identd(8), qmail-header(8) SunOS 5.11 Last change: 2