从String创建RSA公钥

Question

我使用1024 RSA生成了此测试公钥,然后在另一个编码平台中将其编码为DER和Base64.我将密钥复制到Android/Eclipse中的字符串中,我试图使用KeyFactory将其转换为公钥.无论我尝试什么,它都会不断给我一个InvalidKeySpecException.任何建议都将不胜感激.

     private void prepKeys() {
         String AppKeyPub = "MIGHAoGBAOX+TFdFVIKYyCVxWlnbGYbmgkkmHmEv2qStZzAFt6NVqKPLK989Ow0RcqcDTZaZBfO5" +
"5JSVHNIKoqULELruACfqtGoATfgwBp4Owfww8M891gKNSlI/M0yzDQHns5CKwPE01jD6qGZ8/2IZ" +
"OjLJNH6qC9At8iMCbPe9GeXIPFWRAgER";

        // create the key factory          
            try {
                KeyFactory kFactory = KeyFactory.getInstance("RSA");  
                // decode base64 of your key
                byte yourKey[] =  Base64.decode(AppKeyPub,0);
                // generate the public key
                X509EncodedKeySpec spec =  new X509EncodedKeySpec(yourKey);
                PublicKey publicKey = (PublicKey) kFactory.generatePublic(spec);

            System.out.println("Public Key: " + publicKey);  

            } catch (Exception e) {
                // TODO Auto-generated catch block  
                e.printStackTrace(); 
            }

         }

Answer 1

您拥有的密钥是PKCS#1格式,而不是Java接受的SubjectPublicKeyInfo结构.PKCS#1仅是RSA参数的编码,并且缺少诸如算法标识符之类的东西.SubjectPublicKeyInfo在内部使用PKCS#1 - 无论如何都用于RSA公钥.

由于PKCS#1公钥位于SubjectPublicKeyInfo结构的末尾,因此可以简单地为字节添加前缀,使它们成为RSA SubjectPublicKeyInfo.没有像Bouncy Castle这样的额外库,这个解决方案更容易实现.所以,如果您需要没有外部库,那么您可以在这里查看我的答案.

或者,可以编写简单的BER解码器以将结构解码为两个BigInteger值.结构本身并不复杂,但BER/DER长度编码需要一些时间来习惯.

但是,您也可以使用Bouncy Castle(轻量级API)来解决您的问题:

String publicKeyB64 = "MIGHAoGBAOX+TFdFVIKYyCVxWlnbGYbmgkkmHmEv2qStZzAFt6NVqKPLK989Ow0RcqcDTZaZBfO5"
        + "5JSVHNIKoqULELruACfqtGoATfgwBp4Owfww8M891gKNSlI/M0yzDQHns5CKwPE01jD6qGZ8/2IZ"
        + "OjLJNH6qC9At8iMCbPe9GeXIPFWRAgER";
// ok, you may need to use the Base64 decoder of bouncy or Android instead
byte[] decoded = Base64.getDecoder().decode(publicKeyB64);
org.bouncycastle.asn1.pkcs.RSAPublicKey pkcs1PublicKey = org.bouncycastle.asn1.pkcs.RSAPublicKey.getInstance(decoded);
BigInteger modulus = pkcs1PublicKey.getModulus();
BigInteger publicExponent = pkcs1PublicKey.getPublicExponent();
RSAPublicKeySpec keySpec = new RSAPublicKeySpec(modulus, publicExponent);
KeyFactory kf = KeyFactory.getInstance("RSA");
PublicKey generatedPublic = kf.generatePublic(keySpec);
System.out.printf("Modulus: %X%n", modulus);
System.out.printf("Public exponent: %d ... 17? Why?%n", publicExponent); // 17? OK.
System.out.printf("See, Java class result: %s, is RSAPublicKey: %b%n", generatedPublic.getClass().getName(), generatedPublic instanceof RSAPublicKey);

正如您所看到的,它实际上只需要一个类作为接口,尽管当然在Bouncy Castle中支持整个ASN.1/BER解码器功能.

请注意,可能需要将Base 64解码器更改为Android特定的android.util.Base64解码器().此代码在等效的Java运行时上进行了测试.