如何在iPhone/Objective C上找出RSA公钥的模数和指数

Question

有没有办法找出使用SecKeyGeneratePair(一般的安全框架)创建的公钥的模数和指数？

Answer 1

我真的很高兴,但这是我找到的解决方案(不使用任何外部包).

首先,转到Apple的CryptoExercise示例.从那里下载"SecKeyWrapper"课程.该类中有趣的函数是getPublicKeyBits.

链接到示例:http://developer.apple.com/library/ios/#samplecode/CryptoExercise/Introduction/Intro.html

您将收到的位是DER编码(维基)公钥,包含模数和exp.这是一个代码,可以为您解码,非常简单:

- (NSData *)getPublicKeyExp
{
    NSData* pk = [self getPublicKeyBits];
    if (pk == NULL) return NULL;

    int iterator = 0;

    iterator++; // TYPE - bit stream - mod + exp
    [self derEncodingGetSizeFrom:pk at:&iterator]; // Total size

    iterator++; // TYPE - bit stream mod
    int mod_size = [self derEncodingGetSizeFrom:pk at:&iterator];
    iterator += mod_size;

    iterator++; // TYPE - bit stream exp
    int exp_size = [self derEncodingGetSizeFrom:pk at:&iterator];

    return [pk subdataWithRange:NSMakeRange(iterator, exp_size)];
}

- (NSData *)getPublicKeyMod
{
    NSData* pk = [self getPublicKeyBits];
    if (pk == NULL) return NULL;

    int iterator = 0;

    iterator++; // TYPE - bit stream - mod + exp
    [self derEncodingGetSizeFrom:pk at:&iterator]; // Total size

    iterator++; // TYPE - bit stream mod
    int mod_size = [self derEncodingGetSizeFrom:pk at:&iterator];

    return [pk subdataWithRange:NSMakeRange(iterator, mod_size)];
}

- (int)derEncodingGetSizeFrom:(NSData*)buf at:(int*)iterator
{
    const uint8_t* data = [buf bytes];
    int itr = *iterator;
    int num_bytes = 1;
    int ret = 0;

    if (data[itr] > 0x80) {
        num_bytes = data[itr] - 0x80;
        itr++;
    }

    for (int i = 0 ; i < num_bytes; i++) ret = (ret * 0x100) + data[itr + i];

    *iterator = itr + num_bytes;
    return ret;
}