如何在Java中解码DER编码的字符串？

java decoder asn.1

2022-09-02 20:45:47

我正在尝试从数字证书读取自定义扩展。我知道该值是DER编码的GeneralString。有没有一种简单的方法来正确解码它并获取Java字符串？我尝试了以下方法，但“s”在字符串开头包含一些编码元数据作为垃圾字符。

byte[] ext = cert.getExtensionValue("1.2.3.4");
String s= new String(ext);
System.out.println(s);

有没有一种快速简便的方法来做到这一点？或者我真的需要使用一些完整的ASN.1库吗？

谢谢！

答案 1

使用下一页中包含的说明，我进行了一些更改，并且代码对我很好。

从早期的BC版本移植到1.47及更高版本 - The Legion of the Bouncy Castle http://www.bouncycastle.org/wiki/display/JA1/Porting+from+earlier+BC+releases+to+1.47+and+later

private String getExtensionValue(X509Certificate X509Certificate, String oid) throws IOException
{
    String decoded = null;
    byte[] extensionValue = X509Certificate.getExtensionValue(oid);

    if (extensionValue != null)
    {
        ASN1Primitive derObject = toDERObject(extensionValue);
        if (derObject instanceof DEROctetString)
        {
            DEROctetString derOctetString = (DEROctetString) derObject;

            derObject = toDERObject(derOctetString.getOctets());
            if (derObject instanceof ASN1String)
            {
                ASN1String s = (ASN1String)derObject;
                decoded = s.getString();
            }

        }
    }
    return decoded;
}

/**
 * From http://stackoverflow.com/questions/2409618/how-do-i-decode-a-der-encoded-string-in-java
 */
private ASN1Primitive toDERObject(byte[] data) throws IOException
{
    ByteArrayInputStream inStream = new ByteArrayInputStream(data);
    ASN1InputStream asnInputStream = new ASN1InputStream(inStream);

    return asnInputStream.readObject();
}

答案 2

事实证明，对于BouncyCastle来说，这是非常简单的：

private String getExtensionValue(X509Certificate X509Certificate, String oid) throws IOException
{
    String decoded = null;
    byte[] extensionValue = X509Certificate.getExtensionValue(oid);

    if (extensionValue != null)
    {
        DERObject derObject = toDERObject(extensionValue);
        if (derObject instanceof DEROctetString)
        {
            DEROctetString derOctetString = (DEROctetString) derObject;

            derObject = toDERObject(derOctetString.getOctets());
            if (derObject instanceof DERUTF8String)
            {
                DERUTF8String s = DERUTF8String.getInstance(derObject);
                decoded = s.getString();
            }

        }
    }
    return decoded;
}

private DERObject toDERObject(byte[] data) throws IOException
{
    ByteArrayInputStream inStream = new ByteArrayInputStream(data);
    ASN1InputStream asnInputStream = new ASN1InputStream(inStream);

    return asnInputStream.readObject();
}