# AES_DecryptAndVerify

## Syntax

      #include <twl/aes.h>

      #define AES_ENCRYPT_HEADER_SIZE 16

      AESResult AES_DecryptAndVerify(
                  const void* src,
                  u32         srcSize,
                  void*       dst,
                  AESCallback callback,
                  void*       arg );

## Arguments

src | Pointer to ciphertext. Must be 4-byte aligned. In addition, it must point to a location in main memory.
srcSize | Ciphertext size. It must be larger than 0, and less than or equal to `AES_PDATA_SIZE_MAX`.
dst | Pointer to the buffer that will store the plaintext. Must be 4-byte aligned. In addition, it must point to a location in main memory. An area of size srcSize - `AES_SIGN_HEADER_SIZE` bytes is required.
callback | Pointer to the callback function to call when decryption completes. It is possible to specify `NULL`.
arg | User-defined parameter that is passed to the above callback function. Can be any value, including `NULL`.

## Return Values

Returns `AES_RESULT_SUCCESS` if the AES operation was started successfully. Any other return values indicate an error.

## Description

Decrypts and verifies the signature of data that was encrypted using `AES_EncryptAndSign()`.

This uses the key that was selected with `AES_SetKey()` to decrypt and verify the signature of the srcSize bytes starting from src. The decrypted result is written to a region starting at dst whose size is srcSize - `AES_SIGN_HEADER_SIZE` bytes. When the decryption process completes, callback is called, using the decrypted result and arg as arguments. callback is called from the interrupt handler, so it might be called even when interrupts are disabled. Conversely, callback will not be called when interrupts are disabled.

This function returns control immediately once it has started the processing. If processing starts without a problem, this function will return `AES_RESULT_SUCCESS`, but if an error occurs during subsequent processing, it will call callback with the error value and arg as arguments. Note: Error notification using this callback is started from the interrupt handler, so depending on the situation, it is possible that the callback can deliver error notification before control returns from the function.

The decryption key must be set beforehand using `AES_SetKey()`.

## See Also

`AES_EncryptAndSign`

## Revision History

2008/07/11 Added `AES_ENCRYPT_HEADER_SIZE`.
2007/12/25 Initial version.

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