This test specified a valid ECDSA signature and EC key (the same as ecdsa-prime256v1-sha512.pem) The problem however is the signature algorithm is indicated as being RSA PKCS#1 v1.5. Signature verification consequently should fail. $ openssl asn1parse -i < [PUBLIC KEY] 0:d=0 hl=2 l= 89 cons: SEQUENCE 2:d=1 hl=2 l= 19 cons: SEQUENCE 4:d=2 hl=2 l= 7 prim: OBJECT :id-ecPublicKey 13:d=2 hl=2 l= 8 prim: OBJECT :prime256v1 23:d=1 hl=2 l= 66 prim: BIT STRING -----BEGIN PUBLIC KEY----- MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEnLDPaTA9r8dh1ORoe07PA55tNKuWSvgIENjVWKS o1vctUSM6F4iSCobuCKGWLHnvoxf7eHnil9rSFG25lfoceA== -----END PUBLIC KEY----- $ openssl asn1parse -i < [ALGORITHM] 0:d=0 hl=2 l= 13 cons: SEQUENCE 2:d=1 hl=2 l= 9 prim: OBJECT :sha512WithRSAEncryption 13:d=1 hl=2 l= 0 prim: NULL -----BEGIN ALGORITHM----- MA0GCSqGSIb3DQEBDQUA -----END ALGORITHM----- -----BEGIN DATA----- bikyFTMBpO72gOZCiSmtrpiMEI1mijH/VdBImUfXX/gaRr+J6E1kAfAjvm6HaI+814TXhcqEZzV SSstS0ARSyEBApHnnzDMJNkQdk7vnIqlDKm4dsRK1yUA7ECcssTR/1hnUY/ep0iOtdv3gbYpog1 APuEMjWr/5jiQb37VTjD4= -----END DATA----- $ openssl asn1parse -i < [SIGNATURE] 0:d=0 hl=2 l= 71 prim: BIT STRING -----BEGIN SIGNATURE----- A0cAMEQCIEufkeQoUocmGh0ckjz2Gc1SwXXP5/G+YKUljGEDSLo9AiAoxF+QHXHEGymGOOwNaoX X/LDDO7/sWpyBCEa2OSiahA== -----END SIGNATURE-----