无法使用openssl为es gcm设置IV [英] Unable to set IV for aes gcm using openssl

问题描述

我正在尝试使用C ++中OpenSSL提供的AES GCM加密机制，并在此链接上使用示例作为参考：
https://wiki.openssl.org/index.php/EVP_Authenticated_Encryption_and_Decryption

I am trying to use AES GCM encryption mechanism provided by OpenSSL in C++ and using example on this link as reference: https://wiki.openssl.org/index.php/EVP_Authenticated_Encryption_and_Decryption

但是，以下语句给我错误：

However, following statement gives me error:

/* Set IV length if default 12 bytes (96 bits) is not appropriate */
if(1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 16, NULL))
    handleErrors();

我得到的错误是：

错误：未在此范围内声明 EVP_CTRL_GCM_SET_IVLEN。

error: ‘EVP_CTRL_GCM_SET_IVLEN’ was not declared in this scope".

我不明白，为什么我不能将IVLEN设置为16个字节吗？我不想
使用默认值12个字节。任何指针都很好。

I do not understand, why I cannot set IVLEN to 16 bytes? I do not want to use the default value of 12 bytes. Any pointers will be great.

推荐答案

我解决了这个错误，实际上，在示例代码中，初始化加密操作和设置IV长度的顺序如下：

I resolved the error. Actually, in the example code, the order for initializing encryption operation and setting IV length is as follows:

* Initialise the encryption operation. */
if(1 != EVP_EncryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL))
    handleErrors();

/* Set IV length if default 12 bytes (96 bits) is not appropriate */
if(1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 16, NULL))
    handleErrors();

我对这些语句有相反的顺序，即先设置IV长度然后再初始化加密操作。我以为，这些是独立的步骤，顺序无关紧要。但是，也许接口需要在设置任何参数之前知道使用了哪种加密机制。

I had reverse order for these statements i.e. setting IV length first and then initializing encryption operation. I thought, these were independent steps and the order didn't matter. But, maybe, the interface needs to know, which encryption mechanism it has use before setting any parameters.

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