从公钥iOS获取模数和指数

Question

我希望从iOS中的公钥获取Modulus和Exponent。我看过许多不同的网站并看过Apple，但不能让它运转起来。

到目前为止，这是我的代码：

- (void)generateKeyPairPlease
{
OSStatus status = noErr;
NSMutableDictionary *privateKeyAttr = [[NSMutableDictionary alloc] init];
NSMutableDictionary *publicKeyAttr = [[NSMutableDictionary alloc] init];
NSMutableDictionary *keyPairAttr = [[NSMutableDictionary alloc] init];

NSData * publicTag = [NSData dataWithBytes:publicKeyIdentifier
                                    length:strlen((const char *)publicKeyIdentifier)];
NSData * privateTag = [NSData dataWithBytes:privateKeyIdentifier
                                     length:strlen((const char *)privateKeyIdentifier)];



SecKeyRef publicKey = NULL;
SecKeyRef privateKey = NULL;

[keyPairAttr setObject:(__bridge id)kSecAttrKeyTypeRSA
                forKey:(__bridge id)kSecAttrKeyType];
[keyPairAttr setObject:[NSNumber numberWithInt:2048]
                forKey:(__bridge id)kSecAttrKeySizeInBits];

[privateKeyAttr setObject:[NSNumber numberWithBool:YES]
                   forKey:(__bridge id)kSecAttrIsPermanent];
[privateKeyAttr setObject:privateTag
                   forKey:(__bridge id)kSecAttrApplicationTag];

[publicKeyAttr setObject:[NSNumber numberWithBool:YES]
                  forKey:(__bridge id)kSecAttrIsPermanent];
[publicKeyAttr setObject:publicTag
                  forKey:(__bridge id)kSecAttrApplicationTag];

[keyPairAttr setObject:privateKeyAttr
                forKey:(__bridge id)kSecPrivateKeyAttrs];
[keyPairAttr setObject:publicKeyAttr
                forKey:(__bridge id)kSecPublicKeyAttrs];

status = SecKeyGeneratePair((__bridge CFDictionaryRef)keyPairAttr,
                            &publicKey, &privateKey);
//    error handling...

NSData *ppp = [NSData dataWithBytes:publicKey length:strlen((const char *)publicKey)];

NSString *responseString, *responseStringASCII, *responseStringUTF8;

responseStringASCII = [[NSString alloc] initWithData:ppp encoding:NSASCIIStringEncoding];
if (!responseStringASCII)
{

    responseString = [[NSString alloc] initWithData:ppp encoding:NSUTF8StringEncoding];
}
else
{

    responseStringUTF8  = [[NSString alloc] initWithData:ppp encoding:NSUTF8StringEncoding];

    if(responseStringUTF8 != nil && [responseStringUTF8 length] < [responseStringASCII length])
    {
        responseString  =   [responseStringUTF8 retain];
    }
    else
    {
        responseString  =   [responseStringASCII retain];
    }

    [responseStringUTF8 release];
}

publicKeyString = responseString;

if(publicKey) CFRelease(publicKey);
if(privateKey) CFRelease(privateKey);

NSData *exp = [self getPublicKeyExp];
NSData *mod = [self getPublicKeyMod];

NSString *expString = [[NSString alloc] initWithData:exp encoding:NSUTF8StringEncoding];
NSString *modString = [[NSString alloc] initWithData:mod encoding:NSUTF8StringEncoding];

NSLog(@"exponent = %@ \n modulus = %@", expString, modString);
}

- (NSData *)getPublicKeyBits: (NSString*) publicKeyIdentifier {

OSStatus sanityCheck = noErr;
NSData * publicKeyBits = nil;
CFTypeRef pk = NULL;
NSMutableDictionary * queryPublicKey = [[NSMutableDictionary alloc] init];

NSData* publicTag = [publicKeyIdentifier dataUsingEncoding:NSUTF8StringEncoding];

// Set the public key query dictionary.
[queryPublicKey setObject:(__bridge_transfer id)kSecClassKey forKey:(__bridge_transfer id)kSecClass];

[queryPublicKey setObject:publicTag forKey:(__bridge_transfer id)kSecAttrApplicationTag];
[queryPublicKey setObject:(__bridge_transfer id)kSecAttrKeyTypeRSA forKey:(__bridge_transfer id)kSecAttrKeyType];
[queryPublicKey setObject:[NSNumber numberWithBool:YES] forKey:(__bridge_transfer id)kSecReturnData];

// Get the key bits.
sanityCheck = SecItemCopyMatching((__bridge CFDictionaryRef)queryPublicKey, &pk);
if (sanityCheck != noErr)
{
    publicKeyBits = nil;
}
publicKeyBits = (__bridge id)pk;
NSLog(@"public bits %@",publicKeyBits);

return publicKeyBits;
}

- (NSData *)getPublicKeyExp
{
NSData* pk = [self getPublicKeyBits:publicKeyString];
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)];
return pk;
}

- (NSData *)getPublicKeyMod
{
NSData* pk = [self getPublicKeyBits:publicKeyString];
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;
}

但是，当我从相关方法中检索模数和指数时，它们会一直返回NULL吗？