CODEX_Ciphers::ElGamalPublicKey Class Reference

Serializable encapsulation of an ElGamal public key. More...

#include <ElGamal.h>

Inheritance diagram for CODEX_Ciphers::ElGamalPublicKey:

[legend]Collaboration diagram for CODEX_Ciphers::ElGamalPublicKey:

[legend]List of all members.

Public Member Functions
	ElGamalPublicKey ()
	Default constructor, for creating an object to be unmarshalled.
	ElGamalPublicKey (BIGNUM *p, BIGNUM *g, BIGNUM *y)
	Constructor taking components of the key as BIGNUM%s.
	ElGamalPublicKey (const CODEX_ASN1::BigNumber &p, const CODEX_ASN1::BigNumber &g, const CODEX_ASN1::BigNumber &y)
	Constructor taking components of the key as BigNumber%s.
	ElGamalPublicKey (const ElGamalPublicKey &aKey)
	Copy constructor.
virtual	~ElGamalPublicKey ()
	Destructor.
void	operator= (const ElGamalPublicKey &aKey)
	Assignment operator.
const CODEX_ASN1::BigNumber &	p () const
	Prime modulus of the public key.
const CODEX_ASN1::BigNumber &	g () const
	Generator of the multiplicative subgroup of Z_p.
const CODEX_ASN1::BigNumber &	y () const
	g^x for private key x
const BIGNUM *	p1 () const
const BIGNUM *	q () const
ElGamalCipherText *	encrypt (const BIGNUM *message, BIGNUM *k=0) const
	Encrypt a message.
ElGamalSchnorrCipherText *	encryptS (const BIGNUM *message, const CODEX_ASN1::Base &id, const HashFunction &hashFunc, BIGNUM *k=0) const
	Encrypt a message with a Schnorr signature attached.
bool	verifySignature (const ElGamalSignature &signature, const BIGNUM *message) const
	Verify the signature for a message.
int	marshal (unsigned char **pp) const
	Serialize the object.
void *	unmarshal (void *bogus, unsigned char **pp, long length)
	Unserialize the object.
void	toFile (const char *fname) const
	Writes the public key to a file.
void *	fromFile (const char *fname)
	Reads the public key from a file.
bool	initialized () const
Protected Member Functions
void	encryptVals (const BIGNUM *message, BIGNUM *k, BIGNUM *c1, BIGNUM *c2) const
	Helper function for computing encryptions.
Protected Attributes
bool	m_initialized
	Has this object been initialized yet, or is it still blank?

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Detailed Description

Serializable encapsulation of an ElGamal public key.

Definition at line 193 of file ElGamal.h.

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Member Function Documentation

ElGamalCipherText * ElGamalPublicKey::encrypt (  const BIGNUM *  message, BIGNUM *  k = 0 )  const

Encrypt a message. In general, the message should include some sort of padding to defend against attacks exploiting short messages. See, for example, "Why Textbook ElGamal and RSA Encryption are Insecure" by D. Boneh, A. Joux, and P.Q. Nguyen. Parameters: message  Non-null pointer to a BIGNUM containing the message to encrypt. This message must be smaller than the modulus of the public key. k  If not 0, the random encryption exponent will be returned. Returns: A pointer to a new ElGamalCipherText object. Exceptions: BignumNullException  The message is 0 or some memory allocation failed. BignumRandRangeException  There was an error generating the random exponent. BignumModExpException  There was an error during modular exponentiation. BignumModMulException  There was an error during modular multiplication. BignumContextException  Memory allocation failed for a BN_CTX. Definition at line 155 of file ElGamalPublicKey.cc. References encryptVals().

ElGamalSchnorrCipherText * ElGamalPublicKey::encryptS (  const BIGNUM *  message, const CODEX_ASN1::Base &  id, const HashFunction &  hashFunc, BIGNUM *  k = 0 )  const

Encrypt a message with a Schnorr signature attached. In general, the message should include some sort of padding to defend against attacks exploiting short messages. See, for example, "Why Textbook ElGamal and RSA Encryption are Insecure" by D. Boneh, A. Joux, and P.Q. Nguyen. The addition of a Schnorr signature is described in "Security of Signed ElGamal Encryption" by C.P. Schnorr and M. Jakobsson. That scheme defends against adaptive chosen ciphertext attacks. We extend this to an encrypter-aware scheme by adding a unique identifier for the principal that knows the plaintext. Parameters: message  Non-null pointer to a BIGNUM containing the message to encrypt. This message must be smaller than the modulus of the public key. id  serializable object containing an identifier for the encrypting party. hashFunc  A secure hash function. k  If not 0, the random encryption exponent will be returned. Returns: A pointer to a new ElGamalSchnorrCipherText object. Exceptions: BignumNullException  The message is 0 or some memory allocation failed. BignumRandRangeException  There was an error generating the random exponent. BignumModExpException  There was an error during modular exponentiation. BignumModMulException  There was an error during modular multiplication. BignumContextException  Memory allocation failed for a BN_CTX. Definition at line 198 of file ElGamalPublicKey.cc. References encryptVals(), CODEX_ASN1::BigNumber::marshal(), q(), and CODEX_ASN1::BigNumber::value(). Referenced by CODEX_Client::Client::readKey(), and CODEX_Client::Client::writeKey().

void ElGamalPublicKey::encryptVals (  const BIGNUM *  message, BIGNUM *  k, BIGNUM *  c1, BIGNUM *  c2 )  const [protected]

Helper function for computing encryptions. All parameters must be allocated beforehand. Parameters: message  Non-null pointer to a BIGNUM containing the message to encrypt. This message must be smaller than the modulus of the public key. k  Random exponent used to generate ciphertext. If 0, a new random value will be chosen. c1  The first part of the ciphertext c2  The second part of the ciphertext Definition at line 354 of file ElGamalPublicKey.cc. References CODEX_Ciphers::jacobi(), q(), and CODEX_ASN1::BigNumber::value(). Referenced by encrypt(), and encryptS().

void * ElGamalPublicKey::fromFile (  const char *  fname  )

Reads the public key from a file. Parameters: fname  Name of the file from which to read the key Exceptions: FileCannotOpenException  The file fname could not be opened. Definition at line 590 of file ElGamalPublicKey.cc. References p(), and unmarshal().

bool CODEX_ASN1::Base::initialized (   )  const [inline, inherited]

Returns: Has this object been initialized? Definition at line 175 of file Base.h. References CODEX_ASN1::Base::m_initialized. Referenced by CODEX_APSS::SecretManagement::addComputeMsg(), CODEX_APSS::SecretManagement::addEstablishMsg(), CODEX_APSS::SecretManagement::addEstablishResponse(), CODEX_APSS::SecretManagement::addInitMsg(), CODEX_APSS::SecretManagement::addSharing(), CODEX_APSS::SecretManagement::addSubsharing(), CODEX_VSS::Combinatoric< NumT, ThreshT >::apply(), CODEX_Server::ServerState::caKey(), CODEX_KeyService::ClientCreateCallback::ClientCreateCallback(), CODEX_VSS::Combinatoric< NumT, ThreshT >::count(), CODEX_Server::QuorumBuilderAct::handler(), CODEX_APSS::MessageVerifier::handler(), CODEX_KeyService::DelegateResponseVerifier::handler(), CODEX_KeyService::DelegateRequestDistributor::handler(), CODEX_KeyService::ClientMessageVerifier::handler(), CODEX_KeyService::ClientMessageSigner::handler(), CODEX_VSS::SubshareLabel< LabelType >::marshal(), CODEX_KeyService::KeyInfo::marshal(), CODEX_VSS::LabeledShare< ShareType, OneWay >::marshal(), CODEX_VSS::ShareLabel< _ShareType, _OneWay >::marshal(), CODEX_VSS::ModExpFunctionalArgs::marshal(), CODEX_VSS::Combinatoric< NumT, ThreshT >::marshal(), CODEX_KeyService::SignWriteCallback::operator()(), CODEX_KeyService::SignReadCallback::operator()(), CODEX_KeyService::SignCreateCallback::operator()(), CODEX_VSS::ModExpFunctional::operator()(), CODEX_KeyService::ClientReadCallback::operator()(), CODEX_KeyService::ClientCreateCallback::operator()(), CODEX_VSS::Combinatoric< NumT, ThreshT >::operator+=(), CODEX_Server::ServerState::readElGamalShares(), CODEX_VSS::Combinatoric< NumT, ThreshT >::recover(), CODEX_APSS::SecretManagement::sendFinished(), CODEX_Server::ServerState::serviceKey(), CODEX_Server::ServerState::setEGShareCallback(), and CODEX_Server::ServerState::setRSAShareCallback().

const BIGNUM * ElGamalPublicKey::p1 (   )  const

Returns: p-1 Exceptions: BignumNullException  Memory could not be allocated. BignumSubException  An error occurred during subtraction. Definition at line 114 of file ElGamalPublicKey.cc. References CODEX_ASN1::BigNumber::value(). Referenced by CODEX_KeyService::ClientMessageSigner::handler(), and q().

const BIGNUM * ElGamalPublicKey::q (   )  const

Returns: (p-1)/2 Exceptions: BignumNullException  Memory could not be allocated. BignumRshiftException  An error occurred while bit-shifting. Definition at line 134 of file ElGamalPublicKey.cc. References p1(). Referenced by CODEX_APSS::StateInfo::configure(), encryptS(), encryptVals(), and CODEX_Client::Client::readKey().

void ElGamalPublicKey::toFile (  const char *  fname  )  const

Writes the public key to a file. Parameters: fname  Name of the file in which to store the key Exceptions: FileCannotCreateException  The file fname could not be created. Definition at line 568 of file ElGamalPublicKey.cc. References marshal(), and p().

bool ElGamalPublicKey::verifySignature (  const ElGamalSignature &  signature, const BIGNUM *  message )  const

Verify the signature for a message. Parameters: signature  Signature object to verify message  Non-null pointer to a BIGNUM containing the message allegedly signed with signature. The message must be smaller than the modulus of the public key, and might be a digest of a longer message. Returns: Success or failure of the signature verification Exceptions: BignumNullException  The message is 0 or some memory allocation failed. BignumModExpException  There was an error during modular exponentiation. BignumModMulException  There was an error during modular multiplication. BignumContextException  Memory allocation failed for a BN_CTX. Definition at line 428 of file ElGamalPublicKey.cc. References CODEX_ASN1::BigNumber::value().

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

• ElGamal.h
• ElGamalPublicKey.cc

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