Below is an example xml file which describes the public certs of a web-service. The cert is self-signed x509 certificate, encoded as ASN.1 DER. To finalize this standards, we will need to agree on the namespace URL and human-readable name.
====BEGIN EXAMPLE FILE
<?xml version="1.0" encoding="UTF-8"?>
<ocm:RobotMetadata xmlns:ocm="http://robot.googlegroups.com/robot-metadata">
<ocm:RobotName>6410837381322593373-robot@a.appspot.com</ocm:RobotName>
<ds:KeyInfo xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
<ds:KeyName>a1eaceba30c41a428be558ad5e089c11b581e408f</ds:KeyName>
<ds:X509Data> <ds:X509Certificate>MIIDHjCCAgagAwIBAgIIGcVprmKcIMcwDQYJKoZIhvcNAQEFBQAwMjEwMC4GA1UE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</ds:X509Certificate>
</ds:X509Data>
</ds:KeyInfo>
<ds:KeyInfo xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
<ds:KeyName>a1eaceba30c41a428be558ad5e089c11b581e408f</ds:KeyName>
<ds:X509Data> <ds:X509Certificate>MIIDHjCCAgagAwIBAgIIGcVprmKcIMcwDQYJKoZIhvcNAQEFBQAwMjEwMC4GA1UE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</ds:X509Certificate>
</ds:X509Data>
</ds:KeyInfo>
</ocm:RobotMetadata>
====END EXAMPLE FILE
Here is the extracted certificate information
Certificate:
Data:
Version: 3 (0x2)
Serial Number:
19:c5:69:ae:62:9c:20:c7
Signature Algorithm: sha1WithRSAEncryption
Issuer: CN=6410837381322593373-robot.a.appspot.com
Validity
Not Before: Jan 27 23:00:23 2011 GMT
Not After : Jan 29 00:00:23 2011 GMT
Subject: CN=6410837381322593373-robot.a.appspot.com
Subject Public Key Info:
Public Key Algorithm: rsaEncryption
RSA Public Key: (2048 bit)
Modulus (2048 bit):
00:a8:6f:9b:c0:80:70:1f:d3:ca:28:9e:28:ac:7c:
ca:e6:37:09:bb:e6:a6:26:16:b9:b8:7e:2f:74:8e:
07:bd:42:15:2f:34:fa:6f:2f:fa:b7:d3:22:36:2f:
ee:12:6b:43:8a:b9:77:52:8d:c7:af:a8:bb:42:c3:
15:68:7d:78:d8:bc:3e:92:46:e1:5e:a6:79:dd:bc:
30:b1:f0:dc:14:4f:09:3f:2c:7e:12:db:90:b2:6d:
1f:69:71:7c:e3:a1:ef:e8:7c:78:67:87:e8:d3:02:
d3:44:45:f9:70:62:f3:7a:de:04:66:96:00:7a:13:
3c:c3:96:fe:52:23:b8:3e:35:03:8b:58:81:1b:f2:
5d:78:56:43:ee:8a:7c:a7:d4:b9:21:d6:ff:cb:f5:
77:9e:01:32:5f:c9:7d:9d:36:ff:90:2c:07:34:f7:
f3:5e:2b:6f:ec:d9:08:a6:9f:63:96:b4:14:6d:80:
c7:dd:c8:fb:e8:f9:2e:ba:06:95:d4:9f:59:e6:2c:
10:29:1a:96:0b:f4:b9:7c:7e:07:ac:c1:e6:ec:2b:
a5:eb:57:2e:6c:db:5c:4d:70:06:1a:d0:66:39:b1:
39:74:da:a0:5a:f8:70:66:50:2c:d6:72:c9:d6:3c:
71:d2:22:a0:64:31:a1:e2:45:64:19:c3:c9:eb:aa:
e0:0d
Exponent: 65537 (0x10001)
X509v3 extensions:
X509v3 Basic Constraints: critical
CA:FALSE
X509v3 Key Usage: critical
Digital Signature
X509v3 Extended Key Usage: critical
TLS Web Client Authentication
Signature Algorithm: sha1WithRSAEncryption
8b:06:4c:a5:d1:a1:35:3b:32:c8:ca:62:4e:ef:65:88:5d:59:
5e:eb:38:3e:62:6e:83:4c:a7:c2:99:79:a9:37:d6:9e:4c:37:
95:41:86:19:80:4b:90:6e:91:e1:08:ad:8c:49:f4:ce:5d:90:
12:25:fd:ce:96:41:d5:e4:c9:0c:f7:23:66:73:65:2b:6a:99:
f6:03:aa:9b:c8:fc:a0:b9:01:e1:16:39:15:13:97:e9:91:85:
3f:4c:ec:f9:57:d9:7a:d4:85:24:24:2f:03:2b:59:0a:84:e1:
9c:d1:49:2b:83:61:e9:30:71:69:4d:e8:76:e5:b8:14:c0:69:
98:2f:7f:ce:fc:a5:94:d7:0c:29:c2:11:48:b9:a8:c6:2e:09:
b5:a4:7b:e1:3b:c8:a7:db:6e:3c:8e:4d:79:44:be:3f:dd:9d:
ce:2a:e4:0a:3b:fa:c8:96:a6:1a:2c:54:ef:f2:b6:b6:48:98:
de:1f:e6:5a:8b:ff:4e:cd:7e:bf:a4:27:e1:43:fa:35:93:73:
8e:f6:09:3b:e7:c1:1d:63:d7:68:b3:9e:69:9f:6d:10:68:fa:
51:3a:91:bd:34:ef:d2:c7:07:59:53:83:15:4a:cb:4e:ee:dd:
b3:7c:e2:fc:9c:a9:d8:6f:f9:51:be:ad:c8:d7:b6:a6:91:0a:
22:99:1d:82