ios 公钥字符串 rsa

iOS 中使用 RSA 加密和解密需要使用到公钥和私钥，其中公钥可以转换为字符串形式。具体步骤如下：

1. 导入 Security.framework 框架

2. 创建 SecKeyRef 对象

- (SecKeyRef)getPublicKey {
    NSString *publicKeyString = @"MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDcNwJztMj+UyIeHJv6X9F6n/2/2jD6UxvTmJwY8C3q1zDfjTJbX9eW1aLlZa+RfCv5GJjW8VgJdMfR7Vv0X2O4tj3qJ4E4tVvzj+Kg8VQaQ2bPL7Jv5X5b5g5Z5hGp5x5YgldfM6Jy1e+HJGcE0WgDvJIDBj6UO2L0ZwY8D2Q0z0TJr+Iqz1W8lGcC9EwwIDAQAB";
    NSData *data = [[NSData alloc] initWithBase64EncodedString:publicKeyString options:NSDataBase64DecodingIgnoreUnknownCharacters];
    if (!data) {
        return nil;
    }
    NSString *tag = @"com.example.publickey";
    NSMutableDictionary *attributes = [[NSMutableDictionary alloc] initWithObjectsAndKeys:
                                        (__bridge id)kSecClassKey, (__bridge id)kSecClass,
                                        (__bridge id)kSecAttrKeyTypeRSA, (__bridge id)kSecAttrKeyType,
                                        tag, (__bridge id)kSecAttrApplicationTag,
                                        (__bridge id)kSecAttrKeyClassPublic, (__bridge id)kSecAttrKeyClass, nil];
    SecKeyRef keyRef = SecKeyCreateWithData((__bridge CFDataRef)data, (__bridge CFDictionaryRef)attributes, nil);
    return keyRef;
}

3. 将 SecKeyRef 对象转换为公钥字符串

- (NSString *)getPublicKeyString {
    SecKeyRef keyRef = [self getPublicKey];
    if (!keyRef) {
        return nil;
    }
    NSData *data = [self dataFromKey:keyRef];
    NSString *base64String = [data base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];
    return base64String;
}

- (NSData *)dataFromKey:(SecKeyRef)key {
    CFDataRef dataRef = SecKeyCopyExternalRepresentation(key, nil);
    if (!dataRef) {
        return nil;
    }
    NSData *data = (__bridge NSData *)dataRef;
    CFRelease(dataRef);
    return data;
}

以上代码将公钥字符串转换为 SecKeyRef 对象，然后再将 SecKeyRef 对象转换为 NSData 对象，最终使用 base64 编码将 NSData 对象转换为字符串形式。