EditCisco PSIRT Publications
EditCisco PSIRT Response to IOS Rootkits
Rootkits on Cisco IOS DevicesEditReferenced List of MD5 Sums
The following link provides CSV files with the MD5 sum of (supposedly) all released IOS images. Currently (27th of May), the list only covers 12.x releases.
http://www.cisco.com/web/tsweb/psirt/cisco-sr-20080516-rootkits.zipNote: Wide spectrum field tests show that a number of valid IOS images are not covered in the MD5 check sum lists published by Cisco. Accordingly, if an image does not have an entry in the published list, it does not prove the image bogus. An invalid MD5 sum however should be considered prove that the image is corrupted.