Commit afbf867c authored by Jonas Schäfer's avatar Jonas Schäfer
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Merge branch 'feature/xep-0438' into premerge

parents 36ee4ec0 dd15f3f5
......@@ -3,6 +3,7 @@
<!ENTITY OWASP "the <span class='ref'><link url='https://owasp.org/'>Open Web Application Security Project (OWASP)</link></span> <note>The Open Web Application Security Project (OWASP, or OWASP Foundation) is a nonprofit foundation that works to improve the security of software. For further information, see &lt;<link url='https://owasp.org/'>https://owasp.org/</link>&gt;.</note>" >
<!ENTITY owasppasswords "<span class='ref'><link url='https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html'>OWASP Password Storage Cheat Sheet</link></span> <note>OWASP Cheat Sheet Series for password storage &lt;<link url='https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html'>https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html</link>&gt;.</note>" >
<!ENTITY rfc2195 "<span class='ref'><link url='http://tools.ietf.org/html/rfc2195'>RFC 2195</link></span> <note>RFC 2195: IMAP/POP AUTHorize Extension for Simple Challenge/Response &lt;<link url='http://tools.ietf.org/html/rfc2195'>http://tools.ietf.org/html/rfc2195</link>&gt;.</note>" >
<!ENTITY rfc5746 "<span class='ref'><link url='http://tools.ietf.org/html/rfc5746'>RFC 5746</link></span> <note>RFC 5746: Transport Layer Security (TLS) Renegotiation Indication Extension &lt;<link url='http://tools.ietf.org/html/rfc5746'>http://tools.ietf.org/html/rfc5746</link>&gt;.</note>" >
<!ENTITY rfc7677 "<span class='ref'><link url='http://tools.ietf.org/html/rfc7677'>RFC 7677</link></span> <note>RFC 7677: SCRAM-SHA-256 and SCRAM-SHA-256-PLUS Simple Authentication and Security Layer (SASL) Mechanisms &lt;<link url='http://tools.ietf.org/html/rfc7677'>http://tools.ietf.org/html/rfc7677</link>&gt;.</note>" >
<!ENTITY rfc8018 "<span class='ref'><link url='http://tools.ietf.org/html/rfc8018'>RFC 8018</link></span> <note>RFC 8018: PKCS #5: Password-Based Cryptography Specification Version 2.1 &lt;<link url='http://tools.ietf.org/html/rfc8018'>http://tools.ietf.org/html/rfc8018</link>&gt;.</note>" >
<!ENTITY rfc8265 "<span class='ref'><link url='http://tools.ietf.org/html/rfc8265'>RFC 8265</link></span> <note>RFC 8265: Preparation, Enforcement, and Comparison of Internationalized Strings Representing Usernames and Passwords &lt;<link url='http://tools.ietf.org/html/rfc8265'>http://tools.ietf.org/html/rfc8265</link>&gt;.</note>" >
......@@ -31,11 +32,17 @@
<supersededby/>
<shortname>passwords</shortname>
&sam;
<revision>
<version>0.2.0</version>
<date>2020-10-30</date>
<initials>ssw</initials>
<remark><p>Update to match draft-ietf-kitten-password-storage-01.</p></remark>
</revision>
<revision>
<version>0.1.1</version>
<date>2020-05-05</date>
<initials>ssw</initials>
<remark><p>Fix reference to external document</p></remark>
<remark><p>Fix reference to external document.</p></remark>
</revision>
<revision>
<version>0.1.0</version>
......@@ -87,12 +94,30 @@
</section1>
<section1 topic='Glossary' anchor='glossary'>
<p>
Many terms used in this document are defined in &nistsp800-63-3; Appendix
A.1 and in &nistsp800-132; §3.1.
Various security-related terms are to be understood in the sense
defined in &rfc4949;
Some may also be defined in defined in &nistsp800-63-3; Appendix A.1 and in
&nistsp800-132; §3.1.
</p>
<p>
Throughout this document the term "password" is used to mean any password,
passphrase, PIN, or other memorized secret.
</p>
<p>
Other common terms used throughout this document include:
</p>
<dl>
<di>
<dt>Mechanism Pinning</dt>
<dd>
Mechanism pinning A security mechanism which allows SASL clients to
resist downgrade attacks.
Clients that implement mechanism pinning remember the perceived strength
of the SASL mechanism used in a previous successful authentication
attempt and thereafter only authenticate using mechanisms of equal or
higher perceived strength.
</dd>
</di>
<di>
<dt>Pepper</dt>
<dd>
......@@ -101,6 +126,12 @@
They must not be stored alongside the hashed password.
</dd>
</di>
<di>
<dt>Salt</dt>
<dd>
In this document salt is used as defined in &rfc4949;.
</dd>
</di>
</dl>
</section1>
<section1 topic='SASL Mechanisms' anchor='required'>
......@@ -166,6 +197,30 @@
<li>PLAIN</li>
<li>DIGEST-MD5, CRAM-MD5</li>
</ol>
<p>
The EXTERNAL mechanism defined in &rfc4422; appendix A is placed at
the top of the list.
However, its perceived strength depends on the underlying authentication
protocol.
In this example, we assume that TLS (&rfc8446;) services are being used.
</p>
<p>
The channel binding ("-PLUS") variants of SCRAM (&rfc5802;) are listed
above their non-channel binding cousins, but may not always be
available depending on the type of channel binding data available to
the SASL negotiator.
</p>
<p>
The PLAIN mechanism sends the username and password in plain text,
but does allow for the use of a strong key derivation function (KDF)
for the stored version of the password on the server.
</p>
<p>
Finally, the DIGEST-MD5 and CRAM-MD5 mechanisms are listed last
because they use weak hashes and ciphers and prevent the server from
storing passwords using a KDF. For a list of problems with DIGEST-
MD5 see &rfc6331;.
</p>
</section2>
<section2 topic='Storage' anchor='client-storage'>
<p>
......@@ -200,7 +255,7 @@
<section2 topic='Storage' anchor='server-storage'>
<p>
Servers MUST always store passwords only after they have been salted and
hashed.
hashed using a strong KDF.
If multiple hashes are supported for use with SCRAM, for example
SCRAM-SHA-1 and SCRAM-SHA-256, separate salted and hashed passwords SHOULD
be calculated and stored for each mechanism so that users can log in with
......@@ -216,6 +271,25 @@
pepper stored in the application configuration, an environment variable,
or some other location other than the datastore containing the salts.
</p>
<p>
The following minimum restrictions MUST be observed when generating salts
and peppers.
More up to date numbers may be found in &owasppasswords;
</p>
<dl>
<di>
<dt>Minimum Salt Length</dt>
<dd>
16 bytes
</dd>
</di>
<di>
<dt>Minimum Pepper Length</dt>
<dd>
32 bytes
</dd>
</di>
</dl>
</section2>
<section2 topic='Authentication and Rotation' anchor='auth'>
<p>
......@@ -251,16 +325,16 @@
</p>
<dl>
<di>
<dt>Minimum iterations</dt>
<dt>Minimum iteration count (c)</dt>
<dd>10,000 (100,000 for higher security environments)</dd>
</di>
<di>
<dt>Minimum salt length</dt>
<dd>16 bytes</dd>
<dt>Hash</dt>
<dd>SHA256</dd>
</di>
<di>
<dt>Minimum pepper length</dt>
<dd>32 bytes</dd>
<dt>Output length (dkLen)</dt>
<dd>hLen (length of the chosen hash)</dd>
</di>
</dl>
<p>
......@@ -270,17 +344,34 @@
</section1>
<section1 topic='Password Complexity Requirements' anchor='passwordcomplexity'>
<p>
Clients and servers SHOULD enforce a minimum length of 8 characters for user
passwords.
Before any other password complexity requirements are checked, the
preparation and enforcement steps of the OpaqueString profile of &rfc8265;
SHOULD be applied (for more information see the Internationalization
Considerations section).
Entities SHOULD enforce a minimum length of 8 characters for user passwords.
If using a mechanism such as PLAIN where the server performs hashing on the
original password, a maximum length between 64 and 128 characters MAY be
imposed to prevent denial of service (DoS) attacks.
Passwords SHOULD be required to conform to the Opaque String profile of
&rfc8265;.
No other password restrictions should be applied.
Entities SHOULD NOT apply any other password restrictions.
</p>
<p>
In addition to these password complexity requirements, servers SHOULD
maintain a password blocklist and reject attempts by a claimant to use
passwords on the blocklist during registration or password reset.
The contents of this blocklist are a matter of server policy.
Some common recommendations include lists of common passwords that are not
otherwise prevented by length requirements, and passwords present in known
breaches.
</p>
</section1>
<section1 topic='Security Considerations' anchor='security'>
<p>
This document contains recommendations that are likely to change over time.
It should be reviewed regularly to ensure that it remains accurate and up to
date.
Many of the recommendations in this document were taken from
&owasppasswords;, &nistsp800-63b;, and &nistsp800-132;.
</p>
<p>
The SCRAM suite of SASL mechanisms are recommended in this document,
however, there is currently no way to force a password reset.
......@@ -288,6 +379,22 @@
that new, untested, SCRAM-based or SCRAM-like mechanisms should be added
with caution.
</p>
<p>
The "-PLUS" variants of SCRAM support channel binding to their underlying
security layer, but lack a mechanism for negotiating what type of channel
binding to use.
In &rfc5802; the tls-unique (&rfc5929;) channel
binding mechanism is specified as the default, and it is therefore likely to
be used in most applications that support channel binding.
However, in the absence of the TLS extended master secret fix (&rfc7627;)
and the renegotiation indication TLS extension (&rfc5746;) the tls-unique
and tls-server-endpoint channel binding data can be forged by an attacker
that can MITM the connection.
Before advertising a channel binding SASL mechanism, entities MUST ensure
that both the TLS extended master secret fix and the renegotiation
indication extension are in place and that the connection has not been
renegotiated.
</p>
<p>
This document mentions many hash functions that are already in
use in the XMPP ecosystem, or that have been used in the past.
......@@ -297,11 +404,28 @@
implications, see &xep0414;
</p>
<p>
This document contains recommendations that are likely to change over time.
It should be reviewed yearly to ensure that it remains accurate and up to
date.
Many of the recommendations in this document were taken from the
&owasppasswords;, which can be used as a reference when making updates.
For TLS 1.3 no channel binding types are currently defined. Channel binding
SASL mechanisms MUST NOT be advertised or negotiated over a TLS 1.3 channel
until such types are defined.
</p>
</section1>
<section1 topic='Internationalization Considerations' anchor='security'>
<p>
The PRECIS framework (Preparation, Enforcement, and Comparison of
Internationalized Strings) defined in &rfc8264; is used to enforce
internationalization rules on strings and to prevent common application
security issues arrising from allowing the full range of Unicode codepoints
in usernames, passwords, and other identifiers.
The OpaqueString profile of &rfc8265; is used in this document to ensure
that codepoints in passwords are treated carefully and consistently.
This ensures that users typing certain characters on different keyboards
that may provide different versions of the same character will still be able
to log in.
For example, some keyboards may output the full-width version of a character
while other keyboards output the half-width version of the same character.
The Width Mapping rule of the OpaqueString profile addresses this and
ensures that comparison succeeds and the claimant is able to be
authenticated.
</p>
</section1>
<section1 topic='IANA Considerations' anchor='iana'>
......
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