colemanjp/gist:3952297

## gistfile1.md

      
    Raw
  

              gistfile1.md
            
          
    Check key length on dkim for our google apps domain

Get the public key for our selector

$ dig -t txt googleprd._domainkey.yale.edu

; <<>> DiG 9.9.1-P3-RedHat-9.9.1-9.P3.fc17 <<>> -t txt googleprd._domainkey.yale.edu
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12280
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 4, ADDITIONAL: 5

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;googleprd._domainkey.yale.edu. IN      TXT

;; ANSWER SECTION:
googleprd._domainkey.yale.edu. 10800 IN TXT     "v=DKIM1\; k=rsa\; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDpIW0kMkNWgb44eGDpR1ktuixg72kxQUdGWSask4IkaUPN4l1WQb0dc/5xr/7kYxmtZWruFqX7Kf9uToyBPjescCkfJ1s6MfciCTgxgK7lgumuuAnOZ04BJ8PztQmvZTyXM/TqRz6+5TGbstqcQ1N+nBwOp8rj7Xclw8YVKlo2LwIDAQAB"

;; AUTHORITY SECTION:
yale.edu.               10800   IN      NS      serv1.net.yale.edu.
yale.edu.               10800   IN      NS      serv3.net.yale.edu.
yale.edu.               10800   IN      NS      serv4.net.yale.edu.
yale.edu.               10800   IN      NS      serv2.net.yale.edu.

;; ADDITIONAL SECTION:
serv1.net.yale.edu.     10800   IN      A       130.132.1.9
serv2.net.yale.edu.     10800   IN      A       130.132.1.10
serv3.net.yale.edu.     10800   IN      A       130.132.1.11
serv4.net.yale.edu.     10800   IN      A       130.132.89.9

;; Query time: 2 msec
;; SERVER: 130.132.1.9#53(130.132.1.9)
;; WHEN: Thu Oct 25 08:11:00 2012
;; MSG SIZE  rcvd: 453

Format it so that openssl can read it.  Add line breaks at 78

$ cat /tmp/key
-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDpIW0kMkNWgb44eGDpR1ktuixg72kxQUdGWSask
4IkaUPN4l1WQb0dc /5xr/7kYxmtZWruFqX7Kf9uToyBPjescCkfJ1s6MfciCTgxgK7lgumuuAnOZ
04BJ8PztQmvZTyXM/TqRz6+5TGbstqcQ1N+nBwOp8rj7Xclw8YVKlo2LwIDAQAB
-----END PUBLIC KEY-----

Find the key length

$ openssl rsa -noout -text -pubin < /tmp/key
Public-Key: (1024 bit)
Modulus:
    00:e9:21:6d:24:32:43:56:81:be:38:78:60:e9:47:
    59:2d:ba:2c:60:ef:69:31:41:47:46:59:26:ac:93:
    82:24:69:43:cd:e2:5d:56:41:bd:1d:73:fe:71:af:
    fe:e4:63:19:ad:65:6a:ee:16:a5:fb:29:ff:6e:4e:
    8c:81:3e:37:ac:70:29:1f:27:5b:3a:31:f7:22:09:
    38:31:80:ae:e5:82:e9:ae:b8:09:ce:67:4e:01:27:
    c3:f3:b5:09:af:65:3c:97:33:f4:ea:47:3e:be:e5:
    31:9b:b2:da:9c:43:53:7e:9c:1c:0e:a7:ca:e3:ed:
    77:25:c3:c6:15:2a:5a:36:2f
Exponent: 65537 (0x10001)