- djm@cvs.openbsd.org 2010/08/31 11:54:45
[PROTOCOL PROTOCOL.agent PROTOCOL.certkeys auth2-jpake.c authfd.c]
[authfile.c buffer.h dns.c kex.c kex.h key.c key.h monitor.c]
[monitor_wrap.c myproposal.h packet.c packet.h pathnames.h readconf.c]
[ssh-add.1 ssh-add.c ssh-agent.1 ssh-agent.c ssh-keygen.1 ssh-keygen.c]
[ssh-keyscan.1 ssh-keyscan.c ssh-keysign.8 ssh.1 ssh.c ssh2.h]
[ssh_config.5 sshconnect.c sshconnect2.c sshd.8 sshd.c sshd_config.5]
[uuencode.c uuencode.h bufec.c kexecdh.c kexecdhc.c kexecdhs.c ssh-ecdsa.c]
Implement Elliptic Curve Cryptography modes for key exchange (ECDH) and
host/user keys (ECDSA) as specified by RFC5656. ECDH and ECDSA offer
better performance than plain DH and DSA at the same equivalent symmetric
key length, as well as much shorter keys.
Only the mandatory sections of RFC5656 are implemented, specifically the
three REQUIRED curves nistp256, nistp384 and nistp521 and only ECDH and
ECDSA. Point compression (optional in RFC5656 is NOT implemented).
Certificate host and user keys using the new ECDSA key types are supported.
Note that this code has not been tested for interoperability and may be
subject to change.
feedback and ok markus@
diff --git a/PROTOCOL.certkeys b/PROTOCOL.certkeys
index 1d1be13..2f97649 100644
--- a/PROTOCOL.certkeys
+++ b/PROTOCOL.certkeys
@@ -5,31 +5,37 @@
----------
The SSH protocol currently supports a simple public key authentication
-mechanism. Unlike other public key implementations, SSH eschews the
-use of X.509 certificates and uses raw keys. This approach has some
-benefits relating to simplicity of configuration and minimisation
-of attack surface, but it does not support the important use-cases
-of centrally managed, passwordless authentication and centrally
-certified host keys.
+mechanism. Unlike other public key implementations, SSH eschews the use
+of X.509 certificates and uses raw keys. This approach has some benefits
+relating to simplicity of configuration and minimisation of attack
+surface, but it does not support the important use-cases of centrally
+managed, passwordless authentication and centrally certified host keys.
These protocol extensions build on the simple public key authentication
-system already in SSH to allow certificate-based authentication.
-The certificates used are not traditional X.509 certificates, with
-numerous options and complex encoding rules, but something rather
-more minimal: a key, some identity information and usage options
-that have been signed with some other trusted key.
+system already in SSH to allow certificate-based authentication. The
+certificates used are not traditional X.509 certificates, with numerous
+options and complex encoding rules, but something rather more minimal: a
+key, some identity information and usage options that have been signed
+with some other trusted key.
A sshd server may be configured to allow authentication via certified
-keys, by extending the existing ~/.ssh/authorized_keys mechanism
-to allow specification of certification authority keys in addition
-to raw user keys. The ssh client will support automatic verification
-of acceptance of certified host keys, by adding a similar ability
-to specify CA keys in ~/.ssh/known_hosts.
+keys, by extending the existing ~/.ssh/authorized_keys mechanism to
+allow specification of certification authority keys in addition to
+raw user keys. The ssh client will support automatic verification of
+acceptance of certified host keys, by adding a similar ability to
+specify CA keys in ~/.ssh/known_hosts.
-Certified keys are represented using two new key types:
-ssh-rsa-cert-v01@openssh.com and ssh-dss-cert-v01@openssh.com that
-include certification information along with the public key that is used
-to sign challenges. ssh-keygen performs the CA signing operation.
+Certified keys are represented using new key types:
+
+ ssh-rsa-cert-v01@openssh.com
+ ssh-dss-cert-v01@openssh.com
+ ecdsa-sha2-nistp256-cert-v01@openssh.com
+ ecdsa-sha2-nistp384-cert-v01@openssh.com
+ ecdsa-sha2-nistp521-cert-v01@openssh.com
+
+These include certification information along with the public key
+that is used to sign challenges. ssh-keygen performs the CA signing
+operation.
Protocol extensions
-------------------
@@ -47,10 +53,9 @@
New public key formats
----------------------
-The ssh-rsa-cert-v01@openssh.com and ssh-dss-cert-v01@openssh.com key
-types take a similar high-level format (note: data types and
-encoding are as per RFC4251 section 5). The serialised wire encoding of
-these certificates is also used for storing them on disk.
+The certificate key types take a similar high-level format (note: data
+types and encoding are as per RFC4251 section 5). The serialised wire
+encoding of these certificates is also used for storing them on disk.
#define SSH_CERT_TYPE_USER 1
#define SSH_CERT_TYPE_HOST 2
@@ -93,6 +98,26 @@
string signature key
string signature
+ECDSA certificate
+
+ string "ecdsa-sha2-nistp256@openssh.com" |
+ "ecdsa-sha2-nistp384@openssh.com" |
+ "ecdsa-sha2-nistp521@openssh.com"
+ string nonce
+ string curve
+ string public_key
+ uint64 serial
+ uint32 type
+ string key id
+ string valid principals
+ uint64 valid after
+ uint64 valid before
+ string critical options
+ string extensions
+ string reserved
+ string signature key
+ string signature
+
The nonce field is a CA-provided random bitstring of arbitrary length
(but typically 16 or 32 bytes) included to make attacks that depend on
inducing collisions in the signature hash infeasible.
@@ -101,6 +126,9 @@
p, q, g, y are the DSA parameters as described in FIPS-186-2.
+curve and public key are respectively the ECDSA "[identifier]" and "Q"
+defined in section 3.1 of RFC5656.
+
serial is an optional certificate serial number set by the CA to
provide an abbreviated way to refer to certificates from that CA.
If a CA does not wish to number its certificates it must set this
@@ -123,7 +151,8 @@
"valid after" and "valid before" specify a validity period for the
certificate. Each represents a time in seconds since 1970-01-01
00:00:00. A certificate is considered valid if:
- valid after <= current time < valid before
+
+ valid after <= current time < valid before
criticial options is a set of zero or more key options encoded as
below. All such options are "critical" in the sense that an implementation
@@ -137,15 +166,17 @@
the protocol.
signature key contains the CA key used to sign the certificate.
-The valid key types for CA keys are ssh-rsa and ssh-dss. "Chained"
+The valid key types for CA keys are ssh-rsa, ssh-dss and the ECDSA types
+ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521. "Chained"
certificates, where the signature key type is a certificate type itself
are NOT supported. Note that it is possible for a RSA certificate key to
-be signed by a DSS CA key and vice-versa.
+be signed by a DSS or ECDSA CA key and vice-versa.
signature is computed over all preceding fields from the initial string
up to, and including the signature key. Signatures are computed and
encoded according to the rules defined for the CA's public key algorithm
-(RFC4253 section 6.6 for ssh-rsa and ssh-dss).
+(RFC4253 section 6.6 for ssh-rsa and ssh-dss, RFC5656 for the ECDSA
+types).
Critical options
----------------
@@ -222,4 +253,4 @@
of this script will not be permitted if
this option is not present.
-$OpenBSD: PROTOCOL.certkeys,v 1.7 2010/08/04 05:40:39 djm Exp $
+$OpenBSD: PROTOCOL.certkeys,v 1.8 2010/08/31 11:54:45 djm Exp $