从模数和指数生成RSA公钥 [英] Generate RSA Public Key from Modulus and Exponent

问题描述

我希望从Objective-C中的模数和指数生成一个rsa公钥（pem）。此函数可以通过以下方式在Java中完成;

I'm looking to generate a rsa public key (pem) from both the modulus and exponent in Objective-C. This function can be done in Java by the following;

PublicKey publicKey = KeyFactory.getInstance("RSA").generatePublic(new RSAPublicKeySpec(modulus, exponent));

虽然我在iOS平台上写这个时遇到了一些麻烦。我知道 OpenSSL ，但我找不到成功的方法，我仍然无法生成此密钥。还看了 SCZ-BasicEncodingRules-iOS 但这个返回一个NSData值，我试图弄清楚如何尝试将其转换为NSString。

Although I'm having some trouble writing this for the iOS platform. Am aware of OpenSSL, but I couldn't find a successful method and am still unable to generate this key. Also took a look at SCZ-BasicEncodingRules-iOS but this returns a NSData value and I'm stuck trying to figure out how to try convert it to a NSString.

推荐答案

如果你想要要创建.PEM格式，您需要对 berData 方法的输出进行base64编码。您还需要添加页眉和页脚行。

If you want to create a .PEM format you need to base64 encode the output from the berData method. You also need to add the header and footer lines.

测试数据和代码，请参阅 bytesFromHexString ：

Test data and code, see the end of the answer for bytesFromHexString:

NSString *modulusString =  @"c19bccae1e67743fab1c978f03122fb1a78ef05d565a2964728062ad0365e4751b8253df5fd13ab4ecb95c81ff17b91f969e4fb3d8274c30533338684278f6e5548027df775c055943a24a4117b0274c296c68b722c71670d4b21489a3da05d37ba06f2fb771b671a2c746bae4a049dc718fba19a75f1fb8ae1dd715b33d66a3";
NSString *exponentString = @"010001";

NSData *pubKeyModData = bytesFromHexString(modulusString);
NSData *pubKeyExpData = bytesFromHexString(exponentString);
NSArray *keyArray = @[pubKeyModData, pubKeyExpData];

//Given that you are using SCZ-BasicEncodingRules-iOS:
NSData *berData = [keyArray berData];
NSLog(@"berData:\n%@", berData);

NSString *berBase64 = [berData base64EncodedStringWithOptions:0];
NSString *preamble = @"-----BEGIN CERTIFICATE REQUEST-----";
NSString *postamble = @"-----END CERTIFICATE REQUEST-----";
NSString *pem = [NSString stringWithFormat:@"%@\n%@\n%@", preamble, berBase64, postamble];
NSLog(@"pem:\n%@", pem);

测试数据输出：

berData:
30818802 8180c19b ccae1e67 743fab1c 978f0312 2fb1a78e f05d565a 29647280 62ad0365 e4751b82 53df5fd1 3ab4ecb9 5c81ff17 b91f969e 4fb3d827 4c305333 38684278 f6e55480 27df775c 055943a2 4a4117b0 274c296c 68b722c7 1670d4b2 1489a3da 05d37ba0 6f2fb771 b671a2c7 46bae4a0 49dc718f ba19a75f 1fb8ae1d d715b33d 66a30203 010001

pem:
-----BEGIN CERTIFICATE REQUEST-----
  MIGIAoGAwZvMrh5ndD+rHJePAxIvsaeO8F1WWilkcoBirQNl5HUbglPfX9E6tOy5XIH/F7kflp5Ps9gnTDBTMzhoQnj25VSAJ993XAVZQ6JKQRewJ0wpbGi3IscWcNSyFImj2gXTe6BvL7dxtnGix0a65KBJ3HGPuhmnXx+4rh3XFbM9ZqMCAwEAAQ==
-----END CERTIFICATE REQUEST-----

将hex-ascii转换为数据：

Convert hex-ascii to data:

NSData* bytesFromHexString(NSString * aString) {
    NSString *theString = [[aString componentsSeparatedByCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] componentsJoinedByString:nil];

    NSMutableData* data = [NSMutableData data];
    int idx;
    for (idx = 0; idx+2 <= theString.length; idx+=2) {
        NSRange range = NSMakeRange(idx, 2);
        NSString* hexStr = [theString substringWithRange:range];
        NSScanner* scanner = [NSScanner scannerWithString:hexStr];
        unsigned int intValue;
        if ([scanner scanHexInt:&intValue])
            [data appendBytes:&intValue length:1];
    }
    return data;
}

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