EAX< T > Class Template Reference

Implementation of the EAX authenticated cipher. More...

#include <EAX.h>

Inheritance diagram for EAX< T >:

Public Member Functions
	EAX ()
	Constructs a new EAX object for the block cipher T.
Public Member Functions inherited from EAXCommon
size_t	keySize () const
	Default size of the key for this cipher, in bytes. More...
size_t	ivSize () const
	Size of the initialization vector for this cipher, in bytes. More...
size_t	tagSize () const
	Returns the size of the authentication tag. More...
bool	setKey (const uint8_t *key, size_t len)
	Sets the key to use for future encryption and decryption operations. More...
bool	setIV (const uint8_t *iv, size_t len)
	Sets the initialization vector to use for future encryption and decryption operations. More...
void	encrypt (uint8_t *output, const uint8_t *input, size_t len)
	Encrypts an input buffer and writes the ciphertext to an output buffer. More...
void	decrypt (uint8_t *output, const uint8_t *input, size_t len)
	Decrypts an input buffer and writes the plaintext to an output buffer. More...
void	addAuthData (const void *data, size_t len)
	Adds extra data that will be authenticated but not encrypted. More...
void	computeTag (void *tag, size_t len)
	Finalizes the encryption process and computes the authentication tag. More...
bool	checkTag (const void *tag, size_t len)
	Finalizes the decryption process and checks the authentication tag. More...
void	clear ()
	Clears all security-sensitive state from this cipher. More...
Public Member Functions inherited from AuthenticatedCipher
	AuthenticatedCipher ()
	Constructs a new authenticated cipher.
virtual	~AuthenticatedCipher ()
	Destroys this authenticated cipher.
Public Member Functions inherited from Cipher
	Cipher ()
	Constructs a new cipher object.
virtual	~Cipher ()
	Destroys this cipher object. More...

Additional Inherited Members
Protected Member Functions inherited from EAXCommon
	EAXCommon ()
	Constructs a new cipher in EAX mode. More...
void	setBlockCipher (BlockCipher *cipher)
	Sets the block cipher to use for this EAX object. More...

Detailed Description

template<typename T>
class EAX< T >

Implementation of the EAX authenticated cipher.

EAX mode converts a block cipher into an authenticated cipher that uses the block cipher T to encrypt and authenticate.

The size of the key is determined by the underlying block cipher T. The IV is recommended to be 128 bits (16 bytes) in length, but other lengths are supported as well. The default tagSize() is 128 bits (16 bytes) but the EAX specification does allow smaller tag sizes.

The template parameter T must be a concrete subclass of BlockCipher indicating the specific block cipher to use. The block cipher must have a block size of 128 bits. For example, the following creates a EAX object using AES256 as the underlying cipher and then uses it to encrypt and authenticate a plaintext block:

EAX<AES256> eax;
eax.setKey(key, sizeof(key));
eax.setIV(iv, sizeof(iv));
eax.addAuthData(adata, sizeof(adata));
eax.encrypt(ciphertext, plaintext, sizeof(plaintext));
eax.computeTag(tag, sizeof(tag));

The decryption process is almost identical to convert a ciphertext and tag back into plaintext and then check the tag:

EAX<AES256> eax;
eax.setKey(key, sizeof(key));
eax.setIV(iv, sizeof(iv));
eax.addAuthData(adata, sizeof(adata));
eax.decrypt(ciphertext, plaintext, sizeof(plaintext));
if (!eax.checkTag(tag, sizeof(tag))) {
    // The data was invalid - do not use it.
    ...
}

The EAX class can also be used to implement message authentication by omitting the plaintext:

EAX<AES256> eax;
eax.setKey(key, sizeof(key));
eax.setIV(iv, sizeof(iv));
eax.addAuthData(adata1, sizeof(adata1));
eax.addAuthData(adata2, sizeof(adata1));
...
eax.addAuthData(adataN, sizeof(adataN));
eax.computeTag(tag, sizeof(tag));

References: https://en.wikipedia.org/wiki/EAX_mode, http://web.cs.ucdavis.edu/~rogaway/papers/eax.html

See also

EAXCommon, GCM

Definition at line 76 of file EAX.h.

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The documentation for this class was generated from the following files:

• EAX.h
• EAX.cpp