[openssl-users] Modulus field in text display of a certificate

[Mabry Tyson]

I happened to notice what seems to be an output glitch in the textual 
output of a certificate.

I received a copy of the QuoVadis Root CA 2 certificate as a file. When 
I examined the certificate via
     openssl x509 -text -in /tmp/QV.cer    (using OpenSSL 1.0.1 14 Mar 
2012 as installed in Ubuntu 14.04)
I noticed an extra first zero byte of the Modulus was shown, as compared 
to the display of that certificate in Firefox.

> Certificate:
>     Data:
>         Version: 3 (0x2)
>         Serial Number: 1289 (0x509)
>     Signature Algorithm: sha1WithRSAEncryption
>         Issuer: C=BM, O=QuoVadis Limited, CN=QuoVadis Root CA 2
> ...
>        Subject Public Key Info:
>             Public Key Algorithm: rsaEncryption
>                 Public-Key: (4096 bit)
>                 Modulus:
>                     00:9a:18:ca:4b:94:0d:00:2d:af:03:29:8a:f0:0f:
> ...
>                     09:62:04:92:16:10:d8:9e:27:47:fb:3b:21:e3:f8:
>                     eb:1d:5b
I believe there should be 4096/8  = 512 bytes in that modulus. There are 
15 bytes shown per line.  512/15 = 34 with a remainder of 2.  This 
output shows 513 bytes (34 lines plus a remainder of 3).