将NSString转换为SecKeyRef以验证objective-C中的RSA

Question

我想验证iOS 7上的数据。现在我有一个功能：

-(BOOL) PKCSVerifyBytesSHA256withRSA:(NSData*) plainData
                            withSign:(NSData*) signature
                                withKey:(SecKeyRef) public_Key{
        size_t signedHashBytesSize = SecKeyGetBlockSize(public_Key);
        const void* signedHashBytes = [signature bytes];
        size_t hashBytesSize = CC_SHA256_DIGEST_LENGTH;
        uint8_t* hashBytes = malloc(hashBytesSize);
        if (!CC_SHA256([plainData bytes], (CC_LONG)[plainData length], hashBytes)){
            return nil;
        }
        OSStatus status = SecKeyRawVerify(publicKey,
                                          kSecPaddingPKCS1SHA256,
                                          hashBytes,
                                          hashBytesSize,
                                          signedHashBytes,
                                          signedHashBytesSize);
        return status == errSecSuccess;
}

和一把钥匙：

NSString *public_key = @"MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCT2eIq8i/uAHzvwOWhFU9AuRHjPnGq8wD461ZH7N4/LjoRwPaPF3meyyENJgtDr4EyhV9KN77/3VT+87ZpT6QH9w6Q5XwDmM3jhU6bUhWyIPLzrd5XE2rQKRIMXixflz/8Q327VHKsLoKu44HuCh6XrB+uMWUjwVLCLOi2U0sYdQIDAQAB"; 

我建议使用链接here 所以我将- (SecKeyRef)getPublicKeyRef和PKCSVerifyBytesSHA256withRSA添加到新类并调用

RSA1 *rsa1 =[[RSA1 alloc]init];
    if([rsa1 PKCSVerifyBytesSHA256withRSA:Ddata withSign:Dsig withKey:[rsa1 getPublicKeyRef]]){
        NSLog(@"True");}
    else{
        NSLog(@"nil");}

但我收到了错误

size_t signedHashBytesSize = SecKeyGetBlockSize(public_Key);

在PKCSVerifyBytesSHA256withRSA函数中，附注：Thread 1: EXC_BAD_ACCESS(code=1, address=0x10) 有什么方法可以解决这个问题吗？