File transfer and

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File transfer and e-mail FTP and SMTP prtcls FTP Histry 101 The riginal specificatin fr the File Transfer Prtcl was written by Abhay Bhushan (RFC

CS242 Cmputer Netwrks Department f Cmputer Science Wellesley Cllege *Flag day.

Hwever, there are sme imprtant differences. FTP, like HTTP, runs n tp f TCP.

1 File transfer and FTP and SMTP prtcls FTP Histry 101 The riginal specificatin fr the File Transfer Prtcl was written by Abhay Bhushan (RFC 114, April 1971). It ran n NCP until 1980* when it was replaced by a TCP/IP versin (RFC 114). CS242 Cmputer Netwrks Department f Cmputer Science Wellesley Cllege *Flag day. FTP and SMTP 4-2 File Transfer Prtcl (FTP)* FTP and HTTP Like HTTP, FTP is a file transfer prtcl and shares many cmmn characteristics. Hwever, there are sme imprtant differences. FTP, like HTTP, runs n tp f TCP. Hwever, unlike HTTP, FTP uses tw parallel TCP cnnectins t transfer a file, a cntrl cnnectin and a data cnnectin. We say FTP sends its cntrl infrmatin ut-f band. Als unlike HTTP, FTP maintains state. In particular, FTP remembers the current directry and earlier authenticatin. *Fetch n the Mac and Winsck n the PC. FTP and SMTP 4-3 FTP and SMTP 4-4 1

Cntrl and data cnnectin FTP cmmands*, respnses** When a user starts an FTP sessin, the client side f FTP initiates a cntrl TCP cnnectin with the server.

Sample cmmands: sent as ASCII text ver cntrl channel USER username PASS passwrd LIST return list f file in current directry RETR filename retrieves (gets) file STOR filename stres (puts) file nt

2 Cntrl and data cnnectin FTP cmmands*, respnses** When a user starts an FTP sessin, the client side f FTP initiates a cntrl TCP cnnectin with the server. When the server receives a cmmand fr a file transfer, it initiates a TCP data cnnectin. t the client side. The cntrl cnnect stays pen. The data cnnectin stays pen fr ne file nly. Sample cmmands: sent as ASCII text ver cntrl channel USER username PASS passwrd LIST return list f file in current directry RETR filename retrieves (gets) file STOR filename stres (puts) file nt remte hst Sample return cdes status cde and phrase (as in HTTP) 331 Username OK, passwrd required 125 data cnnectin already pen; transfer starting 425 Can t pen data cnnectin 452 Errr writing file *Fur uppercase 7-bit ASCII characters fllwed by sme ptinal arguments. **Replies are three-digit numbers with ptinal message. FTP and SMTP 4-5 FTP and SMTP 4-6 Web brwser supprt Inncence abrad Mst web brwser can retrieve files hsted n FTP servers. FTP URL syntax is described in RFC1738: ftp://[<user>[:<passwrd>]@]<hst>[:<prt>]/<url-path> Fr example, A hst that prvides an FTP service may prvide annymus FTP access. Users lg int the service with an annymus accunt with prmpted fr a user name. Users may be asked t send their address instead f a passwrd, but n verificatin is perfrmed. FTP and SMTP 4-7 FTP and SMTP 4-8 2

Danger Will Rbinsn Getting by in a dangerus wrld FTP was nt designed t be a secure prtcl and it isn t.

perfrm packet capture Explits include: Offline passwrd cracking, spf attacks; and bunce attacks.

This is dne by sending the "AUTH TLS" cmmand.

FTP and SMTP 4-9 FTP and SMTP 4-10 email: The killer app f the seventies Yu ve gt mail In 1971 Ray Tmlinsn sent the first successful email frm ne cmputer,

3 Danger Will Rbinsn Getting by in a dangerus wrld FTP was nt designed t be a secure prtcl and it isn t. It is nt able t encrypt its traffic; all transmissins are in clear text, and usernames, passwrds, cmmands and data can be easily read by anyne able t perfrm packet capture Explits include: Offline passwrd cracking, spf attacks; and bunce attacks. Explicit SFTP is an extensin t the FTP standard that allws clients t request that the FTP sessin be encrypted. This is dne by sending the "AUTH TLS" cmmand. SFTP, SSH* File Transfer Prtcl, is nt related t FTP except that it als transfers files and has a similar cmmand set fr users. *Mre later in the semester. FTP and SMTP 4-9 FTP and SMTP The killer app f the seventies Yu ve gt mail In 1971 Ray Tmlinsn sent the first successful frm ne cmputer, t anther sitting right next t it thrugh ARPANET. He used sign t delineate what hst the user receiving the message was n. Like rdinary mail (and unlike either the HTTP r FTP), is asynchrnus. It has three majr cmpnents: User agents; mail servers; and Simple Mail Transfer Prtcl (SMTP). Tmlinsn can t remember his first message but stated it was QWERTYUIOP r smething similar. FTP and SMTP 4-11 FTP and SMTP

Electrnic mail in the Internet Servers frm the cre Each recipient has a mailbx lcated in ne f the mail servers. User agents allw users read, reply, frward, save, and cmpse messages.

4 Electrnic mail in the Internet Servers frm the cre Each recipient has a mailbx lcated in ne f the mail servers. User agents allw users read, reply, frward, save, and cmpse messages. *Currently, ur brwser acts as a user agent. Frmerly, we used a prprietary agent frm FirstClass. FTP and SMTP 4-13 FTP and SMTP 4-14 SMTP* SMTP (Simple Mail Transfer Prtcl, is the principal applicatin-layer prtcl fr Internet electrnic mail. Like HTTP, SMTP has a client and server side. Bth sides run n every server. Alice sends Bb a message *Smething f a legacy technlgy (RFC 1982), SMTP requires bdy f all mail messages t be in simple seven-bit ASCII. FTP and SMTP 4-15 FTP and SMTP

5 Alice sends Bb a message Alice invkes her user agent, prvides Bb's address, cmpses message, and instructs user agent t send. Alice sends Bb a message Alice's user agent sends the message t her mail server, where it is placed in message queue FTP and SMTP 4-17 FTP and SMTP 4-18 Alice sends Bb a message Client side f SMTP, running n Alice's server sees message, pens TCP cnnectin t SMTP server n Bb's mail server Alice sends Bb a message After initial SMTP handshaking. SMTP client sends Alices's message int TCP cnnectin FTP and SMTP 4-19 FTP and SMTP

6 Alice sends Bb a message Alice sends Bb a message At Bb s mail server, the server side f SMTP receives message Bb invkes his user agent t read the message and puts it int Bb s mailbx FTP and SMTP 4-21 FTP and SMTP 4-22 Sample SMTP interactin [rshull@tempest ~] telnet ALT2.ASPMX.L.GOOGLE.COM 25 Trying Cnnected t ALT2.ASPMX.L.GOOGLE.COM. 220 ********************************************** HELO wellesley.edu 250 mx.ggle.cm at yur service MAIL FROM:<rshull@wellesley.edu> OK q9si wiv.93 - gsmtp RCPT TO:<rshull@wellesley.edu> OK q9si wiv.93 - gsmtp DATA 354 G ahead q9si wiv.93 - gsmtp FROM: Randy Shull <rshull@wellesley.edu> TO: Randy Shull <rshull@wellesley.edu> SUBJECT: Using telnet t yurself I used telnet! OK q9si wiv.93 - gsmtp QUIT clsing cnnectin q9si wiv.93 - gsmtp Cnnectin clsed by freign hst. FTP and SMTP 4-23 SMTP message frmat Frm: rshull@wellesley.edu T: myfriend@crepes.fr Subject: Hme again The message in ASCII Characters nly header bdy *Header lines are part f the message and are different frm the SMTP prtcl cmmands we ve just seen. blank line FTP and SMTP

Only spfing [rshull@tempest ~]$ telnet ALT2.ASPMX.L.GOOGLE.COM 25 Trying 209.85.203.27... Cnnected t ALT2.ASPMX.L.GOOGLE.COM. 220 *********************************************** HELO wellesley.

7 Only spfing ~]$ telnet ALT2.ASPMX.L.GOOGLE.COM 25 Trying Cnnected t ALT2.ASPMX.L.GOOGLE.COM. 220 *********************************************** HELO wellesley.edu 250 mx.ggle.cm at yur service MAIL FROM: <president@wellesley.edu> OK h33si edh gsmtp RCPT TO: <rshull@wellesley.edu> OK h33si edh gsmtp DATA 354 G ahead h33si edh gsmtp FROM: President Jhnsn <president@wellesley.edu> TO: Randy Shull <rshull@wellesley.edu> SUBJECT:Raising yur salary In recgnitin f yur excellent teaching and research I hereby duble yur salary. /Paula. FTP and SMTP 4-25 Shw riginal Delivered-T: rshull@wellesley.edu Received: by with SMTP id c7csp vsg; Thu, 29 Jun :58: (PDT) X-Received: by with SMTP id v8mr edk ; Thu, 29 Jun :58: (PDT) Sme authenticatin signatures here ARC-Authenticatin-Results: i=1; mx.ggle.cm; spf=pass (ggle.cm: dmain f president@wellesley.edu designates as permitted sender) smtp.mailfrm=president@wellesley.edu; dmarc=pass (p=none sp=none dis=none) header.frm=wellesley.edu Return-Path: <president@wellesley.edu> Received: frm wellesley.edu (tempest.wellesley.edu. [ ]) by mx.ggle.cm with SMTP id h33si edh fr rshull@wellesley.edu; Thu, 29 Jun :58: (PDT) Mre authenticatin stuff here Date: Thu, 29 Jun :58: (PDT) Message-Id: <595523bf.e489500a.2058b.d60dSMTPIN_ADDED_MISSING@mx.ggle.cm> FROM: President Jhnsn <president@wellesley.edu> TO: Randy Shull <rshull@wellesley.edu> SUBJECT:Raising yur salary In recgnitin f yur excellent teaching and research I hereby duble yur salary. /Paula FTP and SMTP 4-26 Cmparing HTTP & SMTP Prblem: Hw d we send attachments? Bth transfer files using persistent cnnectins n tp f TCP. HTTP is mainly a pull prtcl, while SMTP is a push prtcl. SMTP requires each message t be 7-bit ASCII. HTTP encapsulates each bject in its wn HTTP message. SMTP places all bjects in ne message. MIME* versin methd used t encde data multimedia data type/subtype parameters encded data Frm: alice@crepes.fr T: bb@hamburger.edu Subject: Picture f yummy crepe. MIME-Versin: 1.0 Cntent-Transfer-Encding: base64 Cntent-Type: image/jpeg base64 encded data base64 encded data *Multipurpse Internet Mail Extensins. FTP and SMTP 4-27 FTP and SMTP

Base64 encding Base64 ER 0 0 1 0 1 1 6 bits Binary input is prcessed in blcks f 3 ctets, r 24 bits.

8 Base64 encding Base64 ER bits Binary input is prcessed in blcks f 3 ctets, r 24 bits. 8 bits 8 bits 8 bits bits bits Each 6 bits in the 24-bit blck is mapped t a printable ASCII character bits Cntent-Type: image/jpeg; name="rshull.jpg" Cntent-Dispsitin: attachment; filename="rshull.jpg" Cntent-Transfer-Encding: base64 X-Attachment-Id: 9j4RC6RXhpZgAATU0AKgAAAAgACQESAAMAAAABAAEAAAESAAMAAAABAAEAAAEaAAU AAAABAAAAegEbAAUAAAABAAAAggEAAMAAAABAAIAAAExAAIAAAAOAAAAigEyAAIA AAAUAAAAmAE8AAIAAAAQAAAArAITAAMAAAABAAEAAAAAALwASAAAAAEAAABIAAAAA QAAUXVpY2tUaW1lIDcuNQAyMDA4OjA5OjA5IDA5OjQxOjM0AE1hYyBPUyBYIDEwLj UuNAAABwEDAAMAAAABAAYAAAEaAAUAAAABAAABFgEbAAUAAAABAAABHgEAAMAAAA BAAIAAAIBAAQAAAABAAABJgICAAQAAAABAAAPjAITAAMAAAABAAEAAAAAAAAASAAA AAEAAABIA... FTP and SMTP 4-29 FTP and SMTP 4-30 Cmmn MIME types Cntent-Type: type/subtype; parameters Text plain; html Image jpeg; gif Audi basic; 32kadpcm Fr example, Vide quicktime Applicatin mswrd; ctet-stream Parameters mdifying subtype Text/plain; charset=us-ascii r text/plain; charset= "ISO " Multipart type SMTP places all bjects in the same message; a Frm: alice@crepes.fr special MIME type is used T: bb@hamburger.edu t tell them apart Subject: Picture f yummy crepe. MIME-Versin: 1.0 Cntent-Type: multipart/mixed; bundary=startofnextpart --StartOfNextPart Dear Bb, Please find a picture f a crepe. --StartOfNextPart Cntent-Transfer-Encding: base64 Cntent-Type: image/jpeg base64 encded data base64 encded data --StartOfNextPart D yu want the recipe? Bundary markers are used t separate bjects Type = Text Subtype = plain FTP and SMTP 4-31 FTP and SMTP

Unanswered questins Mail access prtcls Alice user agent uses SMTP t push e-mail t her mail server. Mail server relays e-mail t Bb. Why the tw step? Hw des Bb s user agent btain his message frm Alice?

9 Unanswered questins Mail access prtcls Alice user agent uses SMTP t push t her mail server. Mail server relays t Bb. Why the tw step? Hw des Bb s user agent btain his message frm Alice? Since SMTL is a PUSH prtcl and Bb wants t PULL his messages, he needs anther applicatin-layer prtcl. There are several t chse frm: Pst Office Prtcl (POP3); Internet Mail Access Prtcl (IMAP); and HTTP. FTP and SMTP 4-33 FTP and SMTP 4-34 POP3 prtcl POP3 is an extremely simple mail access prtcl with rather limited functinality, but it des get the jb dne. Example sessin [w :~] rshull% telnet fc.wellesley.edu 110 Prtcl begins with the user agent pening a TCP cnnectin t the mail server n prt 110. Trying Cnnected t firstclass.wellesley.edu. +OK POP3 server at firstclass.wellesley.edu ready < @firstclass.wellesley.edu> user rshull +OK rshull authenticate please pass dbsabzb +OK rshull's mailbx has 41 messages ( ctets) list +OK 41 messages ( ctets) quit +OK firstclass.wellesley.edu POP3 server clsing cnnectin Cnnectin clsed by freign hst. FTP and SMTP 4-35 FTP and SMTP

10 Example sessin [w :~] rshull% telnet fc.wellesley.edu 110 Example sessin [w :~] rshull% telnet fc.wellesley.edu 110 Cnnected! Trying Cnnected t firstclass.wellesley.edu. +OK POP3 server at firstclass.wellesley.edu ready < @firstclass.wellesley.edu> user rshull +OK rshull authenticate please pass dbsabzb +OK rshull's mailbx has 41 messages ( ctets) list +OK 41 messages ( ctets) quit +OK firstclass.wellesley.edu POP3 server clsing cnnectin Cnnectin clsed by freign hst. authrizatin phase user: declare username pass: passwrd server respnses +OK -ERR Trying Cnnected t firstclass.wellesley.edu. +OK POP3 server at firstclass.wellesley.edu ready < @firstclass.wellesley.edu> user rshull +OK rshull authenticate please pass dbsabzb +OK rshull's mailbx has 41 messages ( ctets) list +OK 41 messages ( ctets) quit +OK firstclass.wellesley.edu POP3 server clsing cnnectin Cnnectin clsed by freign hst. FTP and SMTP 4-37 FTP and SMTP 4-38 Example sessin [w :~] rshull% telnet fc.wellesley.edu 110 IMAP and HTTP transactin phase list: list message numbers retr: retrieve message by number dele: delete quit Trying Cnnected t firstclass.wellesley.edu. +OK POP3 server at firstclass.wellesley.edu ready < @firstclass.wellesley.edu> user rshull +OK rshull authenticate please pass dbsabzb +OK rshull's mailbx has 41 messages ( ctets) list +OK 41 messages ( ctets) quit +OK firstclass.wellesley.edu POP3 server clsing cnnectin Cnnectin clsed by freign hst. POPS is a n frills access prtcl. IMAP is smewhat mre luxurius. Keep all messages n server; allws users t rganize messages int flders; keeps user state acrss sessins (like FC). Alternatively, we culd build an applicatin n tp f HTTP (Gmail, FC, ). FTP and SMTP 4-39 FTP and SMTP

Last Lecture. Start the Application Layer DNS. SUNY at Buffalo; CSE 489/589 Modern Networking Concepts; Fall 2010; Instructor: Hung Q.

Last Lecture. Start the Application Layer DNS. SUNY at Buffalo; CSE 489/589 Modern Networking Concepts; Fall 2010; Instructor: Hung Q. Last Lecture Start the Applicatin Layer DNS SUNY at Buffal; CSE 489/589 Mdern Netwrking Cncepts; Fall 2010; Instructr: Hung Q. Ng 1 This Lecture SMTP SUNY at Buffal; CSE 489/589 Mdern Netwrking Cncepts;