This is an otherwise valid input for ParseCertificate(), however the SEQUENCE tag was changed to be an INTEGER. $ openssl asn1parse -i < [CERTIFICATE] 0:d=0 hl=2 l= 16 prim: INTEGER :300605003002050030020500030200AC -----BEGIN CERTIFICATE----- AhAwBgUAMAIFADACBQADAgCs -----END CERTIFICATE-----