The file s81170-cipher.bin contains data encrypted using the ARIA-128-CBC method.
First decrypt data in the file s81170-cipheredkey.bin. They were encrypted with RSA and can be decrypted with the function RSA_private_decrypt (). Optimal asymmetric encryption padding was used. You must therefore specify RSA_PKCS1_OAEP_PADDING as a parameter. You can work with the function PEM_read_PrivateKey () from the file rsakey.pem.
Now decrypt the data in the file s81170-cipher.bin. The type of the ARIA-128-CBC procedure is returned by the EVP_aria_128_cbc () function in libcrypto. Using the key parameter (key, possibly initialization vector, in this sequence), you have decrypted in the last step. The length of the required parameters can be determined from the type with the functions EVP_CIPHER_key_length () and EVP_CIPHER_iv_length ().
Encrypt the plain text with the cipher CAST5-CFB, the type of which returns the function EVP_cast5_cfb64 (). Using the key parameters (key, possibly initialization vector, in this sequence), the in immediate sequence in the file s81170-key.bin existing.
Save the encrypted data in a file called s81170-result.bin.
Please limit yourself to a source code file s81170.c
