mcrypt_get_iv_size(3) [php man page]

MCRYPT_GET_IV_SIZE(3)							 1						     MCRYPT_GET_IV_SIZE(3)

mcrypt_get_iv_size - Returns the size of the IV belonging to a specific cipher/mode combination

SYNOPSIS

       int mcrypt_get_iv_size (string  $cipher, string	$mode)

DESCRIPTION

	Gets the size of the IV belonging to a specific $cipher/$mode combination.

	It is more useful to use the mcrypt_enc_get_iv_size(3) function as this uses the resource returned by mcrypt_module_open(3).

PARAMETERS

	      o $cipher
		-One of the MCRYPT_ciphername constants, or the name of the algorithm as string.

	      o $mode
		-One  of  the MCRYPT_MODE_modename constants, or one of the following strings: "ecb", "cbc", "cfb", "ofb", "nofb" or "stream". The
		IV is ignored in ECB mode as this mode does not require it. You will need to have the same IV  (think:	starting  point)  both	at
		encryption and decryption stages, otherwise your encryption will fail.

RETURN VALUES

	Returns  the  size  of the Initialization Vector (IV) in bytes. On error the function returns FALSE. If the IV is ignored in the specified
       cipher/mode combination zero is returned.

EXAMPLES

       Example #1

	      mcrypt_get_iv_size(3) Example

	      <?php
		  echo mcrypt_get_iv_size(MCRYPT_CAST_256, MCRYPT_MODE_CFB) . "
";

		  echo mcrypt_get_iv_size('des', 'ecb') . "
";
	      ?>

SEE ALSO

       mcrypt_get_block_size(3), mcrypt_enc_get_iv_size(3), mcrypt_create_iv(3).

PHP Documentation Group 												     MCRYPT_GET_IV_SIZE(3)

MCRYPT_ENCRYPT(3)							 1							 MCRYPT_ENCRYPT(3)

mcrypt_encrypt - Encrypts plaintext with given parameters

SYNOPSIS

       string mcrypt_encrypt (string  $cipher, string  $key, string  $data, string  $mode, [string  $iv])

DESCRIPTION

	Encrypts the data and returns it.

PARAMETERS

	      o $cipher
		-One of the MCRYPT_ciphername constants, or the name of the algorithm as string.

	      o $key
		-  The key with which the data will be encrypted. If it's smaller than the required keysize, it is padded with ' '. It is better
		not to use ASCII strings for keys.  It is recommended to use the mhash functions to create a key from a string.

	      o $data
		- The data that will be encrypted with the given $cipher and $mode. If the size of the data is not n * blocksize, the data will be
		padded with ' '.  The returned crypttext can be larger than the size of the data that was given by $data.

	      o $mode
		-One of the MCRYPT_MODE_modename constants, or one of the following strings: "ecb", "cbc", "cfb", "ofb", "nofb" or "stream".

	      o $iv
		-Used  for  the initialization in CBC, CFB, OFB modes, and in some algorithms in STREAM mode. If you do not supply an IV, while it
		is needed for an algorithm, the function issues a warning and uses an IV with all its bytes set to " ".

RETURN VALUES

	Returns the encrypted data, as a string.

EXAMPLES

       Example #1

	      mcrypt_encrypt(3) Example

	      <?php
		  # --- ENCRYPTION ---

		  # the key should be random binary, use scrypt, bcrypt or PBKDF2 to
		  # convert a string into a key
		  # key is specified using hexadecimal
		  $key = pack('H*', "bcb04b7e103a0cd8b54763051cef08bc55abe029fdebae5e1d417e2ffb2a00a3");

		  # show key size use either 16, 24 or 32 byte keys for AES-128, 192
		  # and 256 respectively
		  $key_size =  strlen($key);
		  echo "Key size: " . $key_size . "
";

		  $plaintext = "This string was AES-256 / CBC / ZeroBytePadding encrypted.";

		  # create a random IV to use with CBC encoding
		  $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
		  $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);

		  # creates a cipher text compatible with AES (Rijndael block size = 128)
		  # to keep the text confidential
		  # only suitable for encoded input that never ends with value 00h
		  # (because of default zero padding)
		  $ciphertext = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key,
					       $plaintext, MCRYPT_MODE_CBC, $iv);

		  # prepend the IV for it to be available for decryption
		  $ciphertext = $iv . $ciphertext;

		  # encode the resulting cipher text so it can be represented by a string
		  $ciphertext_base64 = base64_encode($ciphertext);

		  echo	$ciphertext_base64 . "
";

		  # === WARNING ===

		  # Resulting cipher text has no integrity or authenticity added
		  # and is not protected against padding oracle attacks.

		  # --- DECRYPTION ---

		  $ciphertext_dec = base64_decode($ciphertext_base64);

		  # retrieves the IV, iv_size should be created using mcrypt_get_iv_size()
		  $iv_dec = substr($ciphertext_dec, 0, $iv_size);

		  # retrieves the cipher text (everything except the $iv_size in the front)
		  $ciphertext_dec = substr($ciphertext_dec, $iv_size);

		  # may remove 00h valued characters from end of plain text
		  $plaintext_dec = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key,
						  $ciphertext_dec, MCRYPT_MODE_CBC, $iv_dec);

		  echo	$plaintext_dec . "
";
	      ?>

	      The above example will output:

	      Key size: 32
	      ENJW8mS2KaJoNB5E5CoSAAu0xARgsR1bdzFWpEn+poYw45q+73az5kYi4j+0haevext1dGrcW8Qi59txfCBV8BBj3bzRP3dFCp3CPQSJ8eU=
	      This string was AES-256 / CBC / ZeroBytePadding encrypted.

	See also mcrypt_module_open(3) for a more advanced API and an example.

PHP Documentation Group 													 MCRYPT_ENCRYPT(3)