Java ECC编码的密钥太大

ECC公钥在语义上是曲线上的一个点；如果隐含了您命名的曲线，则X9.62格式的点如果经过压缩，则为67个八位位组（Java字节），如果为未压缩，则为133个八位位组，从没有其他长度。

如果您的意思

java.security.PublicKey.getEnpred()

SubjectPublicKeyInfo

听起来您可能想要X9.62压缩格式，正如我所说的，它是67字节（不是65或66）。如果是这样，您将无法在标准Java
API中控制点压缩，但是考虑到BC提供程序创建了关键对象，BouncyCastle实现类确实支持它。首先将

keypair.getPublicKey()

org.bouncycastle.jcajce.provider.asymmetric.ec.BCECPublicKey

org.bouncycastle.jce.provider.JCEECPublicKey

getQ()

org.bouncycastle.math.ec.ECPoint

getEnpred(booleancompressed)

对于您的另一个但还不是正式的问题，

PublicKey

• 为此曲线和点构造一个ASN.1 / DER编码的SubjectPublicKeyInfo结构（Java称为“ X.509”格式），将其放入

  X509EnpredKeySpec

  并通过适当的运行

  KeyFactory

  。可以使用标准的SunEC提供程序（假定为j7 +，而不是RedHat限制版本）或BC提供程序。通常很难手动构造像SPKI这样的ASN.1编码，但在这种情况下还不错。或如果您拥有BC，则可以使用其ASN.1功能

• 直接致电BC程序做什么欧共体的KeyFactory 将 针对上述输入做

创建点然后使用这三种方式的示例代码：

// as needed in addition to standard java.security and javax.xml import org.bouncycastle.asn1.ASN1EncodableVector;import org.bouncycastle.asn1.DERBitString;import org.bouncycastle.asn1.DERSequence;import org.bouncycastle.asn1.sec.SECObjectIdentifiers;import org.bouncycastle.asn1.x509.AlgorithmIdentifier;import org.bouncycastle.asn1.x9.X962Parameters;import org.bouncycastle.asn1.x9.X9ObjectIdentifiers;import org.bouncycastle.crypto.params.ECPublicKeyParameters;import org.bouncycastle.jcajce.provider.asymmetric.ec.BCECPublicKey;import org.bouncycastle.jcajce.provider.asymmetric.util.EC5Util;import org.bouncycastle.jcajce.provider.asymmetric.util.ECUtil;import org.bouncycastle.jcajce.provider.config.ProviderConfiguration;import org.bouncycastle.jce.provider.BouncyCastleProvider;import org.bouncycastle.math.ec.ECCurve;import org.bouncycastle.math.ec.ECPoint;    KeyPairGenerator kpg = KeyPairGenerator.getInstance("EC", "BC");    kpg.initialize(new ECGenParameterSpec("secp521r1"));    org.bouncycastle.jcajce.provider.asymmetric.ec.BCECPublicKey ku =  (org.bouncycastle.jcajce.provider.asymmetric.ec.BCECPublicKey)kpg.generateKeyPair().getPublic();    byte[] enpredpoint = ku.getQ().getEnpred(true);    { // construct SPKI by hand, this curve only        byte[] hdr = DatatypeConverter.parseHexBinary("3058301006072a8648ce3d020106052b81040023034400");        // could also write out byte[] hdr = {0x30,0x58,0x30,0x10... but items with 0x80 set need casts        if( 0x44  -1 != enpredpoint.length ) throw new Exception ("BAD COMPRESSED POINT FOR secp521r1!");        byte[] spki = Arrays.copyOf(hdr,90); System.arraycopy(enpredpoint,0, spki,0x17, 0x43);        PublicKey k2 = KeyFactory.getInstance("EC" ).generatePublic(new X509EnpredKeySpec(spki));        Signature.getInstance("ECDSA").initVerify(k2); // sanity check    }    { // construct SPKI with BC        AlgorithmIdentifier algid = new AlgorithmIdentifier(X9ObjectIdentifiers.id_ecPublicKey,SECObjectIdentifiers.secp521r1);        ASN1EncodableVector vec = new ASN1EncodableVector();        vec.add(algid); vec.add(new DERBitString(enpredpoint));        byte[] spki = new DERSequence(vec).getEnpred();        PublicKey k2 = KeyFactory.getInstance("EC" ).generatePublic(new X509EnpredKeySpec(spki));        Signature.getInstance("ECDSA").initVerify(k2); // sanity check    }    { // call BC directly        ProviderConfiguration configuration = BouncyCastleProvider.CONFIGURATION;        X962Parameters params = X962Parameters.getInstance(org.bouncycastle.asn1.sec.SECObjectIdentifiers.secp521r1);        ECCurve curve = EC5Util.getCurve(configuration, params);                ECPoint point = curve.deprePoint(enpredpoint).normalize();        ECPublicKeyParameters kparams = new ECPublicKeyParameters(point, ECUtil.getDomainParameters(configuration, params));        PublicKey k2 = new BCECPublicKey ("EC", kparams, configuration);        Signature.getInstance("ECDSA").initVerify(k2); // sanity check    }

相关信息在Java中加载未经压缩的P256
原始64字节长的ECDSA公共密钥。