Challenge 2013 - Certificats X.509 avec signatures identiques

Comment créer 2 certificats X.509 ayant la même signature (md5WithRSAEncryption) mais avec des clés publiques différentes ?

$ openssl x509 -in srv3-cb1.crt -text -noout | tail -n 4
Signature Algorithm: md5WithRSAEncryption
34:f1:98:e4:63:c0:7d:ca:bf:0b:fd:6e:da:9c:58:2d:6f:ec:
0f:18:24:44:15:98:6b:d8:75:4b:6a:06:e3:fd:6b:c0:36:c9:
b6:19:28:cc:b6:c6:bd:47:a2:04:bf:9f
$ openssl x509 -in srv3-cb2.crt -text -noout | tail -n 4
Signature Algorithm: md5WithRSAEncryption
34:f1:98:e4:63:c0:7d:ca:bf:0b:fd:6e:da:9c:58:2d:6f:ec:
0f:18:24:44:15:98:6b:d8:75:4b:6a:06:e3:fd:6b:c0:36:c9:
b6:19:28:cc:b6:c6:bd:47:a2:04:bf:9f

$ sha1sum srv3-cb*.crt
6715e0cfb034f56b323278f13ee6b2616e03955d *srv3-cb1.crt
bc74a32370f7b977e1ab6a1b02e58cdb2c66c590 *srv3-cb2.crt

$ cat ca.crt srv3-cb1.crt >cb1.pem
$ cat ca.crt srv3-cb2.crt >cb2.pem

$ openssl verify -CAfile cb1.pem cb1.pem
cb1.pem: OK

$ openssl verify -CAfile cb2.pem cb2.pem
cb2.pem: OK