Re: pop 110/995, imap 143/993 ?
On 23/08/17 11:13, Joseph Tam wrote: > You don't need plaintext to use CRAM-MD5: there's no problem have *both* > CRAM-MD5 and SSL (it's overkill, but works). And mail data is worth > protecting too. The problem is, as I already pointed out, that using CRAM-MD5 or any other form of challenge-response password mechanism requires that the password be stored on the server in plain text. Furthermore just the advertisement of CRAM-MD5 in a response advertises to an attacker that you do indeed store the passwords as plain text. I would much rather store the password as a hash on the server and only offer up the PLAIN and LOGIN types on an encrypted connection. > No argument here about using end-to-end encryption, but protecting mail > data and metadata is important too. Don't forget also, it's not just > about the privacy (reading) of mail data, but it's also important to > guarantee the authenticity of mail data from tampering. Right, the most common means of doing that is to properly authenticate to the submission server and check TLS validity, then the submission server DKIM signs the message. Of course, this implies trust of the submission server. > By the way, if we assume a hostile network where MITM is possible, then > even closing STARTTLS ports will not guarantee confidential transport: > the MITM attacker can merely open up a fake plaintext-only service port, > then proxy that to the target server. The client must deny non-secured > transport to be fully protected. Yes, exactly! If the client accepts a non-secure connection then it doesn't matter what the server does. It's the client that must be vigilant here. That said, a client that is configured to port 465 would require a config change in order to accept a plaintext connection, but then so would a client that is configured to port 587 and mandatory encryption. Peter
Re: pop 110/995, imap 143/993 ?
Robert Wolf wrote: else (NOT LOCALHOST) and you can see it says LOGINDISABLED unless you have enabled something like cram-md5. Hi, exactly, this is the reason, why plain-text is still needed. You don't need encryption for authentication, if you have secure authentication. Without knowing original password, the MITM cannot generate correct hash for login, so the connection can be plain-text. You don't need plaintext to use CRAM-MD5: there's no problem have *both* CRAM-MD5 and SSL (it's overkill, but works). And mail data is worth protecting too. Of cource, if you then download your emails, the MITM can still read these emails too, if these emails are plain-text (not encrypted using e.g. SMIME or GPG). But he cannot misuse your login. No argument here about using end-to-end encryption, but protecting mail data and metadata is important too. Don't forget also, it's not just about the privacy (reading) of mail data, but it's also important to guarantee the authenticity of mail data from tampering. By the way, if we assume a hostile network where MITM is possible, then even closing STARTTLS ports will not guarantee confidential transport: the MITM attacker can merely open up a fake plaintext-only service port, then proxy that to the target server. The client must deny non-secured transport to be fully protected. Joseph Tam
Re: pop 110/995, imap 143/993 ?
On 22/08/17 20:07, Robert Wolf wrote: > On Tue, 22 Aug 2017, Aki Tuomi wrote: > >> else (NOT LOCALHOST) and you can see it says LOGINDISABLED unless you >> have enabled something like cram-md5. > > exactly, this is the reason, why plain-text is still needed. You don't need > encryption for authentication, if you have secure authentication. Without > knowing original password, the MITM cannot generate correct hash for login, > so > the connection can be plain-text. In order to support non plain-text login types the passwords themselves have to be stored in plain-text. If you use PLAIN but only allow authentication over a secure channel then you get the best of both worlds, you can store your passwords as a hash and they are not transmitted as plain text over the internet. Peter
Re: pop 110/995, imap 143/993 ?
On 22/08/17 18:24, Aki Tuomi wrote: > Dovecot, by default, requires STARTTLS before accepting plaintext > authentication when SSL is configured and you are not connecting from > localhost. You can verify this by telnetting to port 143 from somewhere > else (NOT LOCALHOST) and you can see it says LOGINDISABLED unless you > have enabled something like cram-md5. > > I think postfix, by default, will also prevent authentication without > transport security. No: $ postconf -d smtpd_tls_auth_only smtpd_tls_auth_only = no The commented submission service in master.cf contains it, though, so if you uncomment the service as a whole it will be set: # -o smtpd_tls_auth_only=yes > Also, you should probably using 587/tcp (submission) for sending mail, > instead of 25. Some reputable ISPs prevent connecting to random MX > servers to port 25 to make life harder for spambots. Right, you should never use port 25 for submission, for several reasons. Peter
Re: pop 110/995, imap 143/993 ?
On Tue, 22 Aug 2017, Ivan Warren wrote: > Le 8/22/2017 à 10:03 AM, Robert Wolf a écrit : > > > > WRONG!!! The email is stored plain-text on the first server and then it can > > be > > sent to other few MX servers over plain-text connection. I.e. encrypted > > connection does not protect emails, but the authentication credentials. > > > > > Indeed. > > Encrypted (SSL/TLS) SMTP/IMAP/POP3 sessions only server 1 purpose : To encrypt > authentication. Once a message is sent through a MTA, there is no guarantee of > privacy whatsoever. > > End to End privacy can only be achieved through actual e-mail signing and > encryption (PGP, S/MIME) (but only the message body is encrypted, not the > headers). Hello Ivan yes, headers are not encrypted in plain-text SMTP, the same way as TCP and IP and DNS Requests are not encrypted. One can only hide behind some anonymization system (TOR, Proxy, VPN for TCP, IP, DNS) or some non-presonal mail system to anonymize mail headers to not be able to connect real persones with mail sender/recipient. Regards, Robert.
Re: pop 110/995, imap 143/993 ?
On Tue, 22 Aug 2017, Aki Tuomi wrote: > else (NOT LOCALHOST) and you can see it says LOGINDISABLED unless you > have enabled something like cram-md5. Hi, exactly, this is the reason, why plain-text is still needed. You don't need encryption for authentication, if you have secure authentication. Without knowing original password, the MITM cannot generate correct hash for login, so the connection can be plain-text. Of cource, if you then download your emails, the MITM can still read these emails too, if these emails are plain-text (not encrypted using e.g. SMIME or GPG). But he cannot misuse your login. Regards, Robert Wolf.
Re: pop 110/995, imap 143/993 ?
On Mon, 21 Aug 2017, Gary wrote: > If I read this correctly, starttls will fail due to the MITM attack. That is > the client knows security has been compromised. Using SSL/TLS, the MITM can > use SSL stripping. Since most Postifx conf use "may" for security, the > message would go though unencrypted. Correct??? Hi, many people think, the email is encrypted (secured), because it is sent through encrypted submission connection to client's smtp/submission server. I know some case, where one users sends credit card numbers over encrypted channel to SMTP server and he thinks the card numbers are protected! WRONG!!! The email is stored plain-text on the first server and then it can be sent to other few MX servers over plain-text connection. I.e. encrypted connection does not protect emails, but the authentication credentials. Users should know, that they have to encrypt the email itself, if they want protect it. Regards, Robert Wolf.
Re: Re: pop 110/995, imap 143/993 ?
On 08/22/2017 12:42 AM, Gary wrote: > If I read this correctly, starttls will fail due to the MITM attack. That > is the client knows security has been compromised. [...] Since most Postifx > conf use "may" for security, the message would go though unencrypted. > Correct??? Yup. FWIW, one doesn't need to be a large provider or do full traffic analysis to play this kind of game. A couple years back, my MUA failed to send e-mails while I was using the wifi of a Belgian camping ground. Looking into it, I found that SMTP was transparently redirected to an entirely different server - which did not offer the STARTTLS that I had my MUA insist on, either. Kind regards, -- Jochen Bern Systemingenieur Fon:+49 6151 9067-231 Fax:+49 6151 9067-290 E-Mail: jochen.b...@binect.de www.binect.de www.facebook.de/binect Binect ist ausgezeichnet: Sieger INNOVATIONSPREIS-IT 2017 | Das Büro: Top 100 Büroprodukte 2017 Binect GmbH Robert-Koch-Straße 9, 64331 Weiterstadt, DE Geschäftsführung: Dr. Frank Wermeyer, Nils Manegold Unternehmenssitz: Weiterstadt Register: Amtsgericht Darmstadt, HRB 94685 Umsatzsteuer-ID: DE 221 302 264 MAX 21-Unternehmensgruppe ✁ Diese E-Mail kann vertrauliche Informationen enthalten. Wenn Sie nicht der richtige Adressat sind oder diese E-Mail irrtümlich erhalten haben, informieren Sie bitte sofort den Absender und vernichten Sie diese E-Mail. Das unerlaubte Kopieren, sowie die unbefugte Weitergabe dieser Mail oder von Teilen dieser Mail ist nicht gestattet. Jede von der Binect GmbH versendete Mail ist sorgfältig erstellt worden, dennoch schließen wir die rechtliche Verbindlichkeit aus; sie kann nicht zu einer irgendwie gearteten Verpflichtung zu Lasten der Binect GmbH ausgelegt werden. Wir haben alle verkehrsüblichen Maßnahmen unternommen, um das Risiko der Verbreitung virenbefallener Software oder E-Mails zu minimieren, dennoch raten wir Ihnen, Ihre eigenen Virenkontrollen auf alle Anhänge an dieser Nachricht durchzuführen. Wir schließen, außer für den Fall von Vorsatz oder grober Fahrlässigkeit, die Haftung für jeglichen Verlust oder Schäden durch virenbefallene Software oder E-Mail aus. This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of contents of this e-mail is strictly prohibited. All Binect GmbH emails are created thoroughly, nevertheless we do not accept any legal obligation for the information and wording contained herein. Binect GmbH has taken precautionary measures to reduce the risk of possible distribution of virus infected software or emails. However, we advise you to check attachments to this email for viruses. Except for cases of intent or gross negligence, we cannot accept any legal obligation for loss or damage by virus infected software. smime.p7s Description: S/MIME Cryptographic Signature
Re: pop 110/995, imap 143/993 ?
On 22/08/17 01:56, Peter wrote: Lest anyone think STARTTLS MITM doesn't happen, https://threatpost.com/eff-calls-out-isps-modifying-starttls-encryption-commands/109325/3/ Right, the attack does happen, but it can be prevented by properly configuring the server and client. Not only for security, I prefer port 993/995 as it's just plain simpler to initiate SSL from the get-go rather than to do some handshaking that gets you to the same point. Simpler from a protocol perspective, yes, but not from a configuration perspective. A separate port requires more firewall configuration, requires listening on more one port if you need to accept both plain text and encrypted connections and requires that port to be allocated by IANA. Seriously? So one more port to allow through the firewall is somehow more complex than making sure the server and/or the client is configured to refuse falling back to plaintext communication - and testing various clients and server flavours to make absolutely sure that they do what they are supposed to be doing and don't fall for a MITM attack? At least with plain SSL/TLS ports, you know for sure that if you are connected, it is definitely encrypted. It would appear that STARTTLS is significantly more vulnerable to MITM attacks than plain SSL/TLS for all the above protocols. Is the slight extra convenience of opportunistic encryption really worth the substantial loss in security? I would not say significantly. If the client is configured to require encryption and to validate the resulting cert from the server then any MITM vulnerability of STARTTLS is fully mitigated. A MITM attack is only an issue if the client is configured for opportunistic encryption. Note that the server side should be configured to require encryption on as well, but the important thing is that the client requires it. Yes - and you have a lot of "if's" above - and that is exactly what makes it more vulnerable in practice - where you have to make absolutely sure that your particular version of your particular software definitely behaves like that - while with plain SSL/TLS it just works and there is no checking needed or "if's". In real life, that makes STARTTLS less secure.
Re: pop 110/995, imap 143/993 ?
On 22.08.2017 03:56, Peter wrote: >>> Lest anyone think STARTTLS MITM doesn't happen, >>> >>> https://threatpost.com/eff-calls-out-isps-modifying-starttls-encryption-commands/109325/3/ > Right, the attack does happen, but it can be prevented by properly > configuring the server and client. Dovecot, by default, requires STARTTLS before accepting plaintext authentication when SSL is configured and you are not connecting from localhost. You can verify this by telnetting to port 143 from somewhere else (NOT LOCALHOST) and you can see it says LOGINDISABLED unless you have enabled something like cram-md5. I think postfix, by default, will also prevent authentication without transport security. Also, you should probably using 587/tcp (submission) for sending mail, instead of 25. Some reputable ISPs prevent connecting to random MX servers to port 25 to make life harder for spambots. Aki
Re: pop 110/995, imap 143/993 ?
>> Lest anyone think STARTTLS MITM doesn't happen, >> >> https://threatpost.com/eff-calls-out-isps-modifying-starttls-encryption-commands/109325/3/ Right, the attack does happen, but it can be prevented by properly configuring the server and client. >> Not only for security, I prefer port 993/995 as it's just plain >> simpler to initiate SSL from the get-go rather than to do some >> handshaking that gets you to the same point. Simpler from a protocol perspective, yes, but not from a configuration perspective. A separate port requires more firewall configuration, requires listening on more one port if you need to accept both plain text and encrypted connections and requires that port to be allocated by IANA. Since dovecot, postfix and many other servers already support STARTTLS out of the box, sometimes with *less* configuration for it than the corresponding TLS-only protocol, I would certainly say it's not any simpler from a configuration perspective. That said, neither one is terribly difficult to configure. > Frankly, after reading the above link and some more info on the > internet on the subject, I am now wondering why do we bother at all > with STARTTLS for imap, pop3 Certainly I would agree that it's not needed here, but I do not have a real issue with it, either. > and even smtp ...because SMTP never worked over port 465. 465 is an alternate submission port (despite the name) and no MX server will connect to it. MX to MX traffic always has to happen on port 25 and so the only way to encrypt the stream is via STARTTLS. > (and by the way, port 465 > for SMTP + SSL/TLS *is* indeed deprecated officially)? Yes it is, and I think there was some confusion in this thread earlier about 993/995 not being official, they *are* official, but 465 is not which is probably what led to the confusion. > It would > appear that STARTTLS is significantly more vulnerable to MITM attacks > than plain SSL/TLS for all the above protocols. Is the slight extra > convenience of opportunistic encryption really worth the substantial > loss in security? I would not say significantly. If the client is configured to require encryption and to validate the resulting cert from the server then any MITM vulnerability of STARTTLS is fully mitigated. A MITM attack is only an issue if the client is configured for opportunistic encryption. Note that the server side should be configured to require encryption on as well, but the important thing is that the client requires it. I would like to point out that Thunderbird has not offered opportunistic encryption in its setup for a number of years now, and I think that other clients likely do not as well, so the MITM attack vector is only an issue on older clients that are likely insecure for other reasons as well. Even on those (older) clients you can likely configure them to require encryption, though. > If I read this correctly, starttls will fail due to the MITM attack. > That is the client knows security has been compromised. No, the attack vector is for a client that has encryption set to may. The MITM will either do a plain text connection to the server and strip the STARTTLS capability from the initial server response so that the client does not see it and degrades to plain text, or it will connect via STARTTLS but tunnel that connection to plain text itself, not offering STARTTLS to the client. In either case the client, if configured for opportunistic encryption will happily make the plain text connection to the MITM, or it will refuse the connection if it's configured to require encryption. > Using > SSL/TLS, the MITM can use SSL stripping. Since most Postifx conf use > "may" for security, the message would go though unencrypted. > Correct??? Not really, no. Postfix is set to "may" by default, but this setting is only really used for MX to MX connections because of the number of MX servers that do not support TLS at all. If you look at master.cf at the commented submission service, which is what you would uncomment for submission, you will see that it is configured to not only require encryption but it also will refuse to offer or accept SASL AUTH on a plain text connection. > Is there something to enable for perfect forward security with > starttls? This is actually a client-side issue, but it is pretty much mitigated by the vast majority of modern clients by the fact that they no longer support opportunistic encryption. You either have to select plain text or encrypted, there is no, "encrypt if it is supported" setting any more. Peter
Re: pop 110/995, imap 143/993 ?
Garywrites: If I read this correctly, starttls will fail due to the MITM attack. That is the client knows security has been compromised. I'm not sure what you man by "fail". STARTTLS is prone to MITM attacks if a client has not been configured to refuse non-STARTTLS/SSL sessions. For clients that will allow both secured and plaintext session (like most MTAs), an attacker can strip out the server's STARTTLS capability declaration and fool the client into using an unencrypted session. Using SSL/TLS, the MITM can use SSL stripping. Since most Postifx conf use "may" for security, the message would go though unencrypted. Correct??? If it's what I described above, then yes. Is there something to enable for perfect forward security with starttls? PFS is enabled using a particular choice of encryption algorithms (in particular, use of ephememeral keys algorithms like ECDHE-*), but this happens after SSL initiaton, whether by STARTTLS, or by connection to SSL ports. Joseph Tam
Re: pop 110/995, imap 143/993 ?
If I read this correctly, starttls will fail due to the MITM attack. That is the client knows security has been compromised. Using SSL/TLS, the MITM can use SSL stripping. Since most Postifx conf use "may" for security, the message would go though unencrypted. Correct??? Is there something to enable for perfect forward security with starttls? Original Message From: s.ar...@open-t.co.uk Sent: August 21, 2017 3:07 PM To: dovecot@dovecot.org Reply-to: dovecot@dovecot.org Subject: Re: pop 110/995, imap 143/993 ? On 21/08/17 22:18, Joseph Tam wrote: > > Lest anyone think STARTTLS MITM doesn't happen, > > >https://threatpost.com/eff-calls-out-isps-modifying-starttls-encryption-commands/109325/3/ > > Not only for security, I prefer port 993/995 as it's just plain simpler > to initiate SSL from the get-go rather than to do some handshaking that > gets you to the same point. Frankly, after reading the above link and some more info on the internet on the subject, I am now wondering why do we bother at all with STARTTLS for imap, pop3 and even smtp (and by the way, port 465 for SMTP + SSL/TLS *is* indeed deprecated officially)? It would appear that STARTTLS is significantly more vulnerable to MITM attacks than plain SSL/TLS for all the above protocols. Is the slight extra convenience of opportunistic encryption really worth the substantial loss in security?
Re: pop 110/995, imap 143/993 ?
On 21/08/17 22:18, Joseph Tam wrote: Lest anyone think STARTTLS MITM doesn't happen, https://threatpost.com/eff-calls-out-isps-modifying-starttls-encryption-commands/109325/3/ Not only for security, I prefer port 993/995 as it's just plain simpler to initiate SSL from the get-go rather than to do some handshaking that gets you to the same point. Frankly, after reading the above link and some more info on the internet on the subject, I am now wondering why do we bother at all with STARTTLS for imap, pop3 and even smtp (and by the way, port 465 for SMTP + SSL/TLS *is* indeed deprecated officially)? It would appear that STARTTLS is significantly more vulnerable to MITM attacks than plain SSL/TLS for all the above protocols. Is the slight extra convenience of opportunistic encryption really worth the substantial loss in security?
Re: pop 110/995, imap 143/993 ?
Lest anyone think STARTTLS MITM doesn't happen, https://threatpost.com/eff-calls-out-isps-modifying-starttls-encryption-commands/109325/3/ Not only for security, I prefer port 993/995 as it's just plain simpler to initiate SSL from the get-go rather than to do some handshaking that gets you to the same point. Joseph Tam
Re: pop 110/995, imap 143/993 ?
Bottom line, a server operator's view can be a lot narrower than this, especially in the scenario where you serve the general public and do not control the clients. There is definitely no reason why you wouldn't want to serve ports 993/995. The MITM thing can be used to argue against serving ports 110/143, and some servers indeed do not offer those. But you'll always deal with people who would insist 110/143 is the "right" away. It's nice to provide more than option and you can expect many modern clients to default to requiring STARTTLS, and do proper certificate validation. On my own server I provide only 143, and I control all the clients. So you know my taste on the matter :)
Re: pop 110/995, imap 143/993 ?
On 21/08/17 16:25, Robert Wolf wrote: On Mon, 21 Aug 2017, Sebastian Arcus wrote: On 21/08/17 13:39, Robert Wolf wrote: On Mon, 21 Aug 2017, Sebastian Arcus wrote: On 21/08/17 10:37, Gedalya wrote: On 08/21/2017 07:28 AM, voy...@sbt.net.au wrote: is there a 'preferred way'? should I tell users to use 143 over 993 ? or 993 over 143? or? There is no concrete answer. There are various opinions and feelings about this. The opinion againt 993/995 is that these are not standard ports, Out of curiosity, is there a source for this? It's the first time I hear that 993/995 are not standard ports - and searching on the Internet, I can't find any evidence to back it up? Also, pretty much all email software has been using them for the past 20 years or so. It seems like a curiously high rate of adoption for a non-standard :-) Hello, IMHO the "not standard ports" is meant as "old, useless ports now". So in short, ports 993/995 are IANA officially approved, and thus "standard". Further to this, they are in use by the vast majority of email providers, and as far as I can tell, there are no functional or security disadvantages to using SSL over 993/995 - instead of STARTTLS over 110/143. Hello Sebastian, there are no functional disadvantages *** As I have written, only if some protocol can be used in just plain-text mode, then the SSL ports generate additional encryption load. CPU is probably no problem today, but I have seen some slower SSL connection on higher latence network. I am not SSL profi, but it looks like there is some ACK in SSL after some "SSL packet" which makes slower connection on high latency network, because SSL must wait for packet ACK. In plain-text connection, TCP requires ACK too, but TCP can open big window and send many data at once and wait only for the last ACK. there are no security disadvantages *** Exactly, there is really no security disadvantage to use SSL ports, the encryption is same, resp. there is security advantage to use SSL ports to be sure that every communication is encrypted from start and client cannot send anything plaintext. Hi Rob - thank you for the clarification. It is interesting information.
Re: pop 110/995, imap 143/993 ?
On Mon, 21 Aug 2017, Sebastian Arcus wrote: > On 21/08/17 13:39, Robert Wolf wrote: > > > > On Mon, 21 Aug 2017, Sebastian Arcus wrote: > > > > > > > > On 21/08/17 10:37, Gedalya wrote: > > > > On 08/21/2017 07:28 AM, voy...@sbt.net.au wrote: > > > > > is there a 'preferred way'? should I tell users to use 143 over 993 ? > > > > > or > > > > > 993 over 143? or? > > > > There is no concrete answer. There are various opinions and feelings > > > > about > > > > this. > > > > The opinion againt 993/995 is that these are not standard ports, > > > > > > Out of curiosity, is there a source for this? It's the first time I hear > > > that > > > 993/995 are not standard ports - and searching on the Internet, I can't > > > find > > > any evidence to back it up? Also, pretty much all email software has been > > > using them for the past 20 years or so. It seems like a curiously high > > > rate of > > > adoption for a non-standard :-) > > > > > > Hello, > > > > IMHO the "not standard ports" is meant as "old, useless ports now". > > So in short, ports 993/995 are IANA officially approved, and thus "standard". > Further to this, they are in use by the vast majority of email providers, and > as far as I can tell, there are no functional or security disadvantages to > using SSL over 993/995 - instead of STARTTLS over 110/143. Hello Sebastian, > there are no functional disadvantages *** As I have written, only if some protocol can be used in just plain-text mode, then the SSL ports generate additional encryption load. CPU is probably no problem today, but I have seen some slower SSL connection on higher latence network. I am not SSL profi, but it looks like there is some ACK in SSL after some "SSL packet" which makes slower connection on high latency network, because SSL must wait for packet ACK. In plain-text connection, TCP requires ACK too, but TCP can open big window and send many data at once and wait only for the last ACK. > there are no security disadvantages *** Exactly, there is really no security disadvantage to use SSL ports, the encryption is same, resp. there is security advantage to use SSL ports to be sure that every communication is encrypted from start and client cannot send anything plaintext. Regards, Robert Wolf.
Re: pop 110/995, imap 143/993 ?
On 21/08/17 13:39, Robert Wolf wrote: On Mon, 21 Aug 2017, Sebastian Arcus wrote: On 21/08/17 10:37, Gedalya wrote: On 08/21/2017 07:28 AM, voy...@sbt.net.au wrote: is there a 'preferred way'? should I tell users to use 143 over 993 ? or 993 over 143? or? There is no concrete answer. There are various opinions and feelings about this. The opinion againt 993/995 is that these are not standard ports, Out of curiosity, is there a source for this? It's the first time I hear that 993/995 are not standard ports - and searching on the Internet, I can't find any evidence to back it up? Also, pretty much all email software has been using them for the past 20 years or so. It seems like a curiously high rate of adoption for a non-standard :-) Hello, IMHO the "not standard ports" is meant as "old, useless ports now". So in short, ports 993/995 are IANA officially approved, and thus "standard". Further to this, they are in use by the vast majority of email providers, and as far as I can tell, there are no functional or security disadvantages to using SSL over 993/995 - instead of STARTTLS over 110/143.
Re: pop 110/995, imap 143/993 ?
On Mon, 21 Aug 2017, Sebastian Arcus wrote: > > On 21/08/17 10:37, Gedalya wrote: > > On 08/21/2017 07:28 AM, voy...@sbt.net.au wrote: > > > is there a 'preferred way'? should I tell users to use 143 over 993 ? or > > > 993 over 143? or? > > There is no concrete answer. There are various opinions and feelings about > > this. > > The opinion againt 993/995 is that these are not standard ports, > > Out of curiosity, is there a source for this? It's the first time I hear that > 993/995 are not standard ports - and searching on the Internet, I can't find > any evidence to back it up? Also, pretty much all email software has been > using them for the past 20 years or so. It seems like a curiously high rate of > adoption for a non-standard :-) Hello, IMHO the "not standard ports" is meant as "old, useless ports now". AFAIK at the begining there were only plain-text ports 80, 389, 110, 143, 25, 5222 (XMPP) etc without any encryption. Then SSL was implemented on ports 443, 636, 993, 995, 465, 5223 etc. Later, the STARTTLS feature has been introduced and servers and clients has implemented STARTTLS sometime. Since STARTTLS is used in most clients and servers nowdays, there is no need for SSL port. There is even RFC 2817 for STARTTLS in HTTP. So IMHO all SSL ports are meant to be old, useless now, some Jabber clients describe SSL encryption on port 5223 as "legacy". Pros of STARTTLS is, that you CAN start encryption, if you need it. E.g. for SMTP or LDAP you can use plain text connections without expensive encryption for normal mail transfer (MX-MX) or for searching (LDAP), and client can start encryption, if needed for username+password or cert authentication (SMTP submit or LDAP edit with auth). Of cource for IMAP+POP you have to authenticate everytime, i.e. you need encryption everytime. Pros of SSL port is, you now everytime exactly, that your connection is encrypted, so your password is never sent over plain-text channel. Some servers (services) can be configured to fail correct login, if the login is made through plain-text channel. This is good, because MITM cannot instantly see, if the password is correct or not, but the password goes already plain-text and MITM can test it on secure connection later. Regards, Robert Wolf.
Re: pop 110/995, imap 143/993 ?
On Mon, 21 Aug 2017 11:04:40 +0100, Sebastian Arcus stated: >On 21/08/17 10:37, Gedalya wrote: >> On 08/21/2017 07:28 AM, voy...@sbt.net.au wrote: >>> is there a 'preferred way'? should I tell users to use 143 over 993 ? or >>> 993 over 143? or? >> There is no concrete answer. There are various opinions and feelings about >> this. The opinion againt 993/995 is that these are not standard ports, > >Out of curiosity, is there a source for this? It's the first time I hear >that 993/995 are not standard ports - and searching on the Internet, I >can't find any evidence to back it up? Also, pretty much all email >software has been using them for the past 20 years or so. It seems like >a curiously high rate of adoption for a non-standard :-) One of the places I have found extremely useful over the years is: https://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers It lists the port number, TCP & UDP, description and IANA Status. It also lists multiple use ports; such as 465. Port TCP UDP Description IANA status 143 TCP Assigned Internet Message Access Protocol (IMAP) managementOfficial 465 TCP URL Rendezvous Directory for SSM (Cisco protocol) Official 465 TCP Authenticated SMTP over TLS/SSL (SMTPS) Unofficial 993 TCP Assigned Internet Message Access Protocol over TLS/SSL (IMAPS) Official 995 TCP UDP Post Office Protocol 3 over TLS/SSL (POP3S) Official -- Jerry
Re: pop 110/995, imap 143/993 ?
On 08/21/2017 06:04 PM, Sebastian Arcus wrote: > > On 21/08/17 10:37, Gedalya wrote: >> On 08/21/2017 07:28 AM, voy...@sbt.net.au wrote: >>> is there a 'preferred way'? should I tell users to use 143 over 993 ? or >>> 993 over 143? or? >> There is no concrete answer. There are various opinions and feelings about >> this. >> The opinion againt 993/995 is that these are not standard ports, > > Out of curiosity, is there a source for this? It's the first time I hear that > 993/995 are not standard ports - and searching on the Internet, I can't find > any evidence to back it up? Also, pretty much all email software has been > using them for the past 20 years or so. It seems like a curiously high rate > of adoption for a non-standard :-) What kind of evidence would support a negative? I don't understand. Evidence could demonstrate that something is indeed a standard. "Standard" and common practice are not the same thing. A "Standrd" is a document that describes what practice ought to look like. C has a (series of) standard(s), Perl 5 is not exactly standardized. It's just implemented and documented. Either way, at this point these ports are indeed listed here: https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.txt So perhaps it can be said that those still arguing against it on the basis of it being "non-standrd" are still arguing against officially assigning these port numbers, because the old ports are perfectly good, even after the assignment has already been listed by IANA.
Re: pop 110/995, imap 143/993 ?
On 21/08/17 10:37, Gedalya wrote: On 08/21/2017 07:28 AM, voy...@sbt.net.au wrote: is there a 'preferred way'? should I tell users to use 143 over 993 ? or 993 over 143? or? There is no concrete answer. There are various opinions and feelings about this. The opinion againt 993/995 is that these are not standard ports, Out of curiosity, is there a source for this? It's the first time I hear that 993/995 are not standard ports - and searching on the Internet, I can't find any evidence to back it up? Also, pretty much all email software has been using them for the past 20 years or so. It seems like a curiously high rate of adoption for a non-standard :-)
Re: pop 110/995, imap 143/993 ?
On 08/21/2017 07:28 AM, voy...@sbt.net.au wrote: > is there a 'preferred way'? should I tell users to use 143 over 993 ? or > 993 over 143? or? There is no concrete answer. There are various opinions and feelings about this. The opinion againt 993/995 is that these are not standard ports, and there is no need to allocate new ports for the secure version of each protocol since we can use STARTTLS. The problem with 110/143 is that security depends on settings on both ends: The client must be configured to negotiate STARTTLS as mandatory, and refuse to talk to the server when that doesn't work. The server must also refuse to talk to clients without STARTTLS. Since some mail clients support "opportunistic" STARTTLS, that is, use port 143 and use STARTTLS *if / when* available, some people feel there are too many subtleties involved, and ports 993/995 just make all this go away. Requiring STARTTLS on the server side doesn't prevent a man-in-the-middle attack. The client must be configured to insist on negotiating STARTTLS with a server with a verified certificate. > my current understanding is that some (MS?) clients might not support > StartTLS/143 ? so best to offer both ? Their newest clients do support STARTTLS. I don't remember exactly but maybe Outlook 2003 or so didn't support it. > I think? some public WiFi block 993/995 but allow 143/110, hence, another > advantage for using 143/110 Never heard of this either.
Re: pop 110/995, imap 143/993 ?
On 21/08/17 00:28, voy...@sbt.net.au wrote: just setting a new Dovecot server to migrate from older system, but, I have a general question: 1. I've set the server with self issued cert, and both pop/imap StartTLS/110/143 SSL/993/995 (apologies if I'm using wrong naming terminology) is there a 'preferred way'? should I tell users to use 143 over 993 ? or 993 over 143? or? I believe the recommended way for years has been to use the encrypted/SSL versions of both IMAP and POP3 - so ports 993 and 995 respectively. Otherwise you are effectively sending data in plain text over the internet. my current understanding is that some (MS?) clients might not support StartTLS/143 ? so best to offer both ? As far as I know, all popular email clients of the last 15 years, that I can think of, support POP3 on 995 and IMAP on 993 with SSL. I think? some public WiFi block 993/995 but allow 143/110, hence, another advantage for using 143/110 I never heard about his, Maybe others have. I guess this would be even more of a reason to use the encrypted versions of the protocols.
Re: pop 110/995, imap 143/993 ?
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Mon, 21 Aug 2017, voy...@sbt.net.au wrote: 1. I've set the server with self issued cert, and both pop/imap StartTLS/110/143 SSL/993/995 (apologies if I'm using wrong naming terminology) That's fine. - -- Steffen Kaiser -BEGIN PGP SIGNATURE- Version: GnuPG v1 iQEVAwUBWZp0pnz1H7kL/d9rAQIHfgf+Jj+y5Tm2h+13bI3qdsMTo5Yih6fCJlUl pK5Gunj1o4TNKVDQFq4xa0GUTs5G9+uWyfCiOyIwe8GH6auMxmOKqGTScwjdjRxg FVbmzxrLEB1XLoSCVpnuyoCIDZHTBJNdLBWvABBSnSDGV9ZusDvb0/5TzaEoFhlE kLrSj+wGiBMGlAaYoVAECy0oIakzCvV6InSk/c3A09RlwKUxypCdUqYXM01Eba1j EavikirKdL1YYMe7tXhsuomiA4gk9wSpDTzHhQgvZyTrESsrnFgm2rI+6Hnir8Iz cT8C9evkLQVYj8gNqXiTYadj2rutG5G9lotvMlQLcnobpFynvRf7hw== =T5a0 -END PGP SIGNATURE-