postfix ssl errors in log, what does they mean?

[Marko Weber | ZBF]

hello ,

i find many of these in my mail.log:
May 16 14:27:33 mail opendkim[2926]: 119CA2FB20: s=dktest 
d=porcupine.org SSL error:04091068:rsa routines:INT_RSA_VERIFY:bad 
signature

is my openssl broken or something else glitchy? or does this mean the 
dkim from porcupine.org ist invalid?

thanks,

marko