KeyUsage does not allow digital signatures

I’m trying to send HTTPS request from my Java EE program to the host that requires certificate authentication. I have a proper keystore file, truststore with imported CA, the listing of both shows that certificates are inside.

But I receive the following error:

javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: KeyUsage does not allow digital signatures
    at ...

...

Caused by: sun.security.validator.ValidatorException: KeyUsage does not allow digital signatures
    at sun.security.validator.EndEntityChecker.checkTLSServer(EndEntityChecker.java:270)
    at sun.security.validator.EndEntityChecker.check(EndEntityChecker.java:141)
    at sun.security.validator.Validator.validate(Validator.java:264)
    at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:326)
    at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:231)
    at     sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:126)
at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1319)
... 29 more

Viewing the certificate contents in the part of Extensions I see the following:

Extensions:

#1: ObjectId: 2.5.29.14 Criticality=false
SubjectKeyIdentifier [
KeyIdentifier [
0000: 33 87 72 1D 09 2F DF FF   1A A7 D1 C0 E1 CF C5 FA  3.r../..........
0010: A4 19 54 2E                                        ..T.
]
]

#2: ObjectId: 2.16.840.1.113730.1.1 Criticality=false
NetscapeCertType [
   SSL client
]

#3: ObjectId: 2.5.29.35 Criticality=false
AuthorityKeyIdentifier [
KeyIdentifier [
0000: 74 9F 43 07 CC 75 FA D3   D0 13 0F 65 36 CC 4A 9A  t.C..u.....e6.J.
0010: E0 8E 9C 52                                        ...R
]
]

#4: ObjectId: 2.5.29.31 Criticality=false
CRLDistributionPoints [
  [DistributionPoint:
     [URIName: http://test.az:7447/Test%20CA.crl]
]]

#5: ObjectId: 2.5.29.15 Criticality=true
KeyUsage [
  DigitalSignature
]

So my certificate does contain KeyUsage [ DigitalSignature ]

The code snippet of the place throwing the exception looks like the following:

private final static int KU_SIGNATURE = 0;

...

private void checkTLSServer(X509Certificate cert, String parameter)
        throws CertificateException {
    Set<String> exts = getCriticalExtensions(cert);

    ...

    } else if (KU_SERVER_SIGNATURE.contains(parameter)) {
        if (checkKeyUsage(cert, KU_SIGNATURE) == false) {
            throw new ValidatorException
                    ("KeyUsage does not allow digital signatures",
                    ValidatorException.T_EE_EXTENSIONS, cert);
        }
    }

    ...
}

and checkKeyUsage function:

private boolean checkKeyUsage(X509Certificate cert, int bit)
        throws CertificateException {
    boolean[] keyUsage = cert.getKeyUsage();
    if (keyUsage == null) {
        return true;
    }
    return (keyUsage.length > bit) && keyUsage[bit];
}

it fails in return (keyUsage.length > bit) && keyUsage[bit];

The question is why the result of above expression = false? When bit = 0 and cert.getKeyUsage() must return an array of boolean [true, false, false, false, false, false, false, false, false]

Answer

The error actually comes from verifying the server’s certificate. That certificate has a key usage section that doesn’t include a digitalSignature bit.

Some cipher suites require the digital signature bit, specifically Diffie-Hellman key exchange (DHE_RSA and ECDHE_RSA). You may be able to avoid this error by avoiding those cipher types. Otherwise the server certificate needs to support it.

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Answer