Encryption and decryption

[vermarajeev]

Hello guys,
I have written functionality to encrypt and decrypt the file using perl script. Now I want to port this script to crypto++ libaray functionality.
Here is the perl script code,
//For encryption

my $cipher = Crypt::CBC->new(
		-cipher => "Crypt::Rijndael",
		-key    => $key,
		-header => 'salt',
		);
	$cipher->start( 'encrypting' );
 
	while ( read( $original_file, $buffer, 1024 ) ) {
		print $encrypted_file
				$cipher->crypt( $buffer );
	}

my $cipher = Crypt::CBC->new(
		-cipher => "Crypt::Rijndael",
		-key    => $key,
		-header => 'salt',
		);
	$cipher->start( 'encrypting' );

	while ( read( $original_file, $buffer, 1024 ) ) {
		print $encrypted_file
				$cipher->crypt( $buffer );
	}

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//For decryption

my $cipher = Crypt::CBC->new(
		-cipher => "Crypt::OpenSSL::AES",
		-key    => $key,
		-header => 'salt',
		);
	$cipher->start( 'decrypting' );
 
	while ( read( $encrypted_file, $buffer, 1024 ) ) {
		print $decrypted_file
			$cipher->crypt( $buffer );
	}

my $cipher = Crypt::CBC->new(
		-cipher => "Crypt::OpenSSL::AES",
		-key    => $key,
		-header => 'salt',
		);
	$cipher->start( 'decrypting' );

	while ( read( $encrypted_file, $buffer, 1024 ) ) {
		print $decrypted_file
			$cipher->crypt( $buffer );
	}

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I can find the alternative to Crypt::Rijndael in crypto++ lib, but what is the alternative to Crypt::OpenSSL::AES in crypto++ library.

Thanks in advance,

[jacek]

I can find the alternative to Crypt::Rijndael in crypto++ lib, but what is the alternative to Crypt::OpenSSL::AES in crypto++ library.

Rijndael is AES.

[vermarajeev]

Rijndael is AES.

Hi Jacek,
Thank you for your reply.

I know Rijndael is AES but what about "Crypt::OpenSSL::AES" while decrypting the file?
The encrypted file should be compatible with OpenSSL.

[wysota]

AES is AES, no matter which library implements it.

[vermarajeev]

Ok for a while I forget about perl script.

Here is a basic question about encryption/decryption.

I encrypt a file with AES::CBC mode using a random IV( Initialization Vector ). Now how do I get back the same IV for decrypting the encrypted file?

If I use my defined hard coded IV I'm able to decode the file with no problem (as I know what the IV is) but I want to use a random IV to encrypt a file and then want to decrypt the encrypted file.

The pseudo can is something like this

void encryptFile( const char* password, const char* inFile, const char* outFile)
{
     //Get random IV named iv
     //Digest the password named pass
     AES::Encryption aesEncryption(pass, CryptoPP::AES::DEFAULT_KEYLENGTH); 
     CBC_Mode_ExternalCipher::Encryption cbcEncryption(aesEncryption, iv);  
     //Encrypt the file
}
 
void decryptFile( const char* password, const char* inFile, const char* outFile)
{
     //Now to decrypt the encrypted file I need to have the same IV
     // with which the file was encrypted to decrypt it.
     //I dont know how to get it
 
     //Get the IV from the encrypted file
     //digest the password
     //Finally decrypt the encrypted file.
 
}

void encryptFile( const char* password, const char* inFile, const char* outFile)
{
     //Get random IV named iv
     //Digest the password named pass
     AES::Encryption aesEncryption(pass, CryptoPP::AES::DEFAULT_KEYLENGTH); 
     CBC_Mode_ExternalCipher::Encryption cbcEncryption(aesEncryption, iv);  
     //Encrypt the file
}

void decryptFile( const char* password, const char* inFile, const char* outFile)
{
     //Now to decrypt the encrypted file I need to have the same IV
     // with which the file was encrypted to decrypt it.
     //I dont know how to get it
 
     //Get the IV from the encrypted file
     //digest the password
     //Finally decrypt the encrypted file.

}

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In the above code I dont know how to get the same IV by which the file was encrypted. Any idea?

If possible please give your answers taking crypto++ library in view.

Thanks.

[wysota]

As far as I understand it, you can't. You just have to know it, like make it a part of the ciphertext