What strings are allowed in the “common name” attribute in an X.509 certificate?

Question

In the common name field of the DN of a X509 certificate, as defined in ASN.1 notation for OID \"2.5.4.3\", what are the allowed values?

I know that the limit i

Answer 1

Whilst the above answers cover what you'll usually find in there, don't forget that because this is X.509 you can actually put pretty much anything in there. The certificate below for example uses 0.9.2342.19200300.100.1.5 which is 'favourite drink' (See http://www.alvestrand.no/objectid/0.9.2342.19200300.100.1.5.html). Openssl understand this, so the common name is displayed as CN=example.com/emailAddress=test@example.com/favouriteDrink=tequila. There are many other fields that can be put in the certificate common name.

You can use openssl x509 -text to verify that the certificate displays as I've described.

-----BEGIN CERTIFICATE-----
MIIDOzCCAiOgAwIBAgIBCzANBgkqhkiG9w0BAQUFADCBqzEmMCQGA1UEAxMdV2Vz
dHBvaW50IENlcnRpZmljYXRlIFRlc3QgQ0ExEzARBgNVBAgTCkxhbmNhc2hpcmUx
CzAJBgNVBAYTAlVLMR0wGwYJKoZIhvcNAQkBFg5jYUBleGFtcGxlLmNvbTFAMD4G
A1UEChM3V2VzdHBvaW50IENlcnRpZmljYXRlIFRlc3QgUm9vdCBDZXJ0aWZpY2F0
aW9uIEF1dGhvcml0eTAeFw0xMTA3MzEyMTAxMTdaFw0yMTA3MjgyMTAxMTdaMFAx
FDASBgNVBAMTC2V4YW1wbGUuY29tMR8wHQYJKoZIhvcNAQkBFhB0ZXN0QGV4YW1w
bGUuY29tMRcwFQYKCZImiZPyLGQBBRMHdGVxdWlsYTCBnzANBgkqhkiG9w0BAQEF
AAOBjQAwgYkCgYEAuCqI3aNbSkRpA9VuGOmeVQ010Oaawsz4tcW2FQChJDOv6PuT
ucy5IijvaVewotDjnuVzPpBVW5EmC8Qapradomhb6FtFPyH/hGSnhLtht3Ln6stJ
ZkAjvr/wjWDy+3Gy/P5r5weUNWVm2AaQgk2xumx49EIXyzwOEHAhqTE7iEECAwEA
AaNIMEYwCQYDVR0TBAIwADA5BggrBgEFBQcBAQQtMCswKQYIKwYBBQUHMAGGHWh0
dHA6Ly9vY3NwLmV4YW1wbGUuY29tOjg4ODgvMA0GCSqGSIb3DQEBBQUAA4IBAQBL
oz035PphO4yUx7FJVaZjxLgTM4wLrcn2ONGm015/ECO+1Uxj3hWb6/EIDDKV/4e8
x0HDF69zyawYLD1th5tBcZLkV/Dat/Tzkt3boLOCGo2I1P+yjqxlb7BZCk7PEs3+
zjWF2hMcXtAwOIrsRuvXp4eTGwigKLAt/H02US/fa2dXFbOnz91V7oH8ZvynIl/n
hpELPzVWX/pBnHEGA9Bi0jviCKuvQisfaJ8XCiA73qH6CkSoZ2fClnrs+pJNj8i6
vtcMx8htn7FsyB3puVww86JSQ+VDKlQkFbPVla/4Aavzwz8djjVYEWwSgm+tw3jB
zUP/k5Aln5cXNo50KOip
-----END CERTIFICATE-----