Groovy SSL签名验证:签名长度不正确？

我正在尝试使用提供的公钥和签名验证使用私钥签名的邮件.

像魅力一样工作的命令行是

cat call.blah | openssl dgst -sha256 -verify public-key.pem -signature signature.sig
Verified OK

public-key.pem是使用该命令从X509证书创建的

openssl x509 -pubkey -noout -in x509key.cer > public-key.pem

现在我试图模仿groovy,这是我的代码

static void main(String[] args) {

   /* Verify a DSA signature */

    if (args.length != 3) {
        System.out.println("Usage: VerSig publickeyfile signaturefile datafile")
    } else try {

        /* import encoded public key */

        FileInputStream keyfis = new FileInputStream(args[0])

        CertificateFactory f = CertificateFactory.getInstance("X.509")
        X509Certificate certificate = (X509Certificate)f.generateCertificate(keyfis)
        PublicKey pubKey = certificate.getPublicKey()

        /* input the signature bytes */
        FileInputStream sigfis = new FileInputStream(args[1])
        byte[] sigToVerify = new byte[sigfis.available()]
        sigfis.read(sigToVerify)

        sigfis.close()

        /* create a Signature object and initialize it with the public key */
        Signature sig = Signature.getInstance("SHA256withRSA")
        sig.initVerify(pubKey)

        /* Update and verify the data */

        FileInputStream datafis = new FileInputStream(args[2])
        BufferedInputStream bufin = new BufferedInputStream(datafis)

        byte[] buffer = new byte[1024]
        int len
        while (bufin.available() != 0) {
            len = bufin.read(buffer)
            sig.update(buffer, 0, len)
        }

        bufin.close()


        boolean verifies = sig.verify(sigToVerify) // <---- THIS IS WHERE THE ERROR OCCURS

        System.out.println("signature verifies: " + verifies)


    } catch (Exception e) {
        e.printStackTrace()
    }

}

我用这些参数运行它

x509key.cer signature.sig call.blah

(这是X509证书,签名和签名的邮件正文)

获取以下堆栈跟踪

java.security.SignatureException: Signature length not correct: got 512 but was expecting 256
at sun.security.rsa.RSASignature.engineVerify(RSASignature.java:190)
at java.security.Signature$Delegate.engineVerify(Signature.java:1174)
at java.security.Signature.verify(Signature.java:624)
at java_security_Signature$verify$2.call(Unknown Source)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:45)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:108)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
at VerSig.main(VerSign.groovy:50)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)

我究竟做错了什么？