AES/CBC 和 AES/ECB 加密后的数据大小 [英] Size of data after AES/CBC and AES/ECB encryption

问题描述

我想知道 AES 加密后的数据大小，这样我就可以避免缓冲我的 AES 后数据(在磁盘或内存上)，主要是为了知道大小.

I would like to know the size of data after AES encryption so that I can avoid buffering my post-AES data(on disk or memory) mainly for knowing the size.

我使用 128 位 AES 和 javax.crypto.Cipher 和 javax.crypto.CipherInputStream 进行加密.

I use 128 bit AES and javax.crypto.Cipher and javax.crypto.CipherInputStream for encryption.

对不同输入大小进行的一些测试表明，如下计算的后加密大小是正确的:

A few tests performed with various input sizes show that, the post encryption size calculated as below is correct:

long size = input_Size_In_Bytes; 
long post_AES_Size = size + (16 - (size % 16));

但我不确定上述公式是否适用于所有可能的输入尺寸.

But I am not sure whether the above formula is applicable for all possible input sizes.

有没有一种方法可以计算应用 AES 加密后的数据大小 - 无需预先缓冲加密数据(在磁盘或内存上)以了解其加密后的大小?

Is there a way to calculate the size of data after applying AES encryption – in advance without having to buffer the encrypted data(on disk or memory) to know its post-encryption size?

推荐答案

AES 具有 16 字节的固定块大小，而不管密钥大小.假设您使用 PKCS 5/7 填充，请使用此公式，

AES has a fixed block size of 16-bytes regardless key size. Assuming you use PKCS 5/7 padding, use this formula,

 cipherLen = (clearLen/16 + 1) * 16;

请注意，如果明文是块大小的倍数，则需要一个全新的块进行填充.假设您的明文是 16 个字节.密文将占用 32 个字节.

Please note that if the clear-text is multiple of block size, a whole new block is needed for padding. Say you clear-text is 16 bytes. The cipher-text will take 32 bytes.

您可能想用密文存储 IV(初始向量).在这种情况下，您需要为 IV 添加 16 个字节.

You might want to store IV (Initial Vector) with cipher-text. In that case, you need to add 16 more bytes for IV.

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