A typical method is to use PKCS#7 padding. On 12/12/2012 9:07 AM, Hailei Hu wrote:
Hi, everyone! I am testing openssl AES encrypt and decrypt using AES_cbc_encrypt. for example, I have a file which has 10 bytes, after using AES_cbc_encrypt, the encrypted file become 16 bytes. But when I use anohter program to decrypt this encrypted file using AES_cbc_encrypt, How could I know the correct decrypted file size? Because according to the declaration of AES_cbc_encrypt:void AES_cbc_encrypt (const unsigned char *in, unsigned char *out, const unsigned long length, const AES_KEY *key, /* it will be changed during the encrypt&decrypt process, so it required to be reset each time */ unsigned char *ivec, /* salt, it will be changed during the encrypt&decrypt process, so it required to be reset each time */ const int enc /*AES_ENCRYPT for encrypt and other values for descrypt*/ ); when I call this function, param "length" is the encrypted file size. But I think the decrypted file size should be less than "param length". So How could I know how many bytes I should read from "out" to write to a decrypted file ?
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