member

Member functionality. More...

Data Structures
struct	MemberPrecomp
	Pre-computed member settings. More...
struct	PreComputedSignature
	Pre-computed signature. More...

Functions
EpidStatus	EpidMemberCreate (GroupPubKey const *pub_key, PrivKey const *priv_key, MemberPrecomp const *precomp, BitSupplier rnd_func, void *rnd_param, MemberCtx **ctx)
	Creates a new member context. More...
void	EpidMemberDelete (MemberCtx **ctx)
	Deletes an existing member context. More...
EpidStatus	EpidMemberWritePrecomp (MemberCtx const *ctx, MemberPrecomp *precomp)
	Serializes the pre-computed member settings. More...
EpidStatus	EpidMemberSetHashAlg (MemberCtx *ctx, HashAlg hash_alg)
	Sets the hash algorithm to be used by a member. More...
size_t	EpidGetSigSize (SigRl const *sig_rl)
	Computes the size in bytes required for a Intel(R) EPID signature. More...
EpidStatus	EpidSign (MemberCtx const *ctx, void const *msg, size_t msg_len, void const *basename, size_t basename_len, SigRl const *sig_rl, size_t sig_rl_size, EpidSignature *sig, size_t sig_len)
	Writes a Intel(R) EPID signature. More...
EpidStatus	EpidRegisterBaseName (MemberCtx *ctx, void const *basename, size_t basename_len)
	Registers a basename with a member. More...
EpidStatus	EpidAddPreSigs (MemberCtx *ctx, size_t number_presigs, PreComputedSignature *presigs)
	Extends the member's pool of pre-computed signatures. More...
size_t	EpidGetNumPreSigs (MemberCtx const *ctx)
	Gets the number of pre-computed signatures in the member's pool. More...
EpidStatus	EpidWritePreSigs (MemberCtx *ctx, PreComputedSignature *presigs, size_t number_presigs)
	Serializes pre-computed signatures from the member's pool. More...
EpidStatus	EpidRequestJoin (GroupPubKey const *pub_key, IssuerNonce const *ni, FpElemStr const *f, BitSupplier rnd_func, void *rnd_param, HashAlg hash_alg, JoinRequest *join_request)
	Creates a request to join a group. More...
EpidStatus	EpidSignBasic (MemberCtx const *ctx, void const *msg, size_t msg_len, void const *basename, size_t basename_len, BasicSignature *sig)
	Creates a basic signature for use in constrained environment. More...
EpidStatus	EpidNrProve (MemberCtx const *ctx, void const *msg, size_t msg_len, BasicSignature const *sig, SigRlEntry const *sigrl_entry, NrProof *proof)
	Calculates a non-revoked proof for a single signature based revocation list entry. More...
bool	EpidIsPrivKeyInGroup (GroupPubKey const *pub_key, PrivKey const *priv_key)
	Tests if a member private key is valid without checking revocation. More...
EpidStatus	EpidDecompressPrivKey (GroupPubKey const *pub_key, CompressedPrivKey const *compressed_privkey, PrivKey *priv_key)
	Decompresses compressed member private key. More...

Detailed Description

Member functionality.

Defines the APIs needed by Intel(R) EPID members. Each member context (MemberCtx) represents membership in a single group.

Function Documentation

EpidStatus EpidAddPreSigs	(	MemberCtx *	ctx,
		size_t	number_presigs,
		PreComputedSignature *	presigs
	)

Extends the member's pool of pre-computed signatures.

Can either generate new pre-computed signatures or import existing ones. EpidWritePreSigs can be used to export pre-computed signatures.

Parameters

[in]	ctx	The member context.
[in]	number_presigs	The number of pre-computed signatures to add to the internal pool.
[in,out]	presigs	Optional array of valid pre-computed signatures to import. If presigs is not NULL it most contain at least number_presigs pre-computed signatures.

Returns

EpidStatus

Note

presigs buffer is zeroed out before return to prevent pre-computed signatures from being reused.

If the result is not kEpidNoErr the state of the pre-computed signature pool, and of presigs, is undefined.

See also

EpidMemberCreate

EpidWritePreSigs

EpidStatus EpidDecompressPrivKey	(	GroupPubKey const *	pub_key,
		CompressedPrivKey const *	compressed_privkey,
		PrivKey *	priv_key
	)

Decompresses compressed member private key.

Converts a compressed member private key into a member private key for use by other member APIs.

Parameters

[in]	pub_key	The public key of the group.
[in]	compressed_privkey	The compressed member private key to be decompressed.
[out]	priv_key	The member private key.

Returns

EpidStatus

Examples:

signmsg.c.

size_t EpidGetNumPreSigs

(

MemberCtx const *

ctx

)

Gets the number of pre-computed signatures in the member's pool.

Parameters

[in]

ctx

The member context.

Returns

Number of remaining pre-computed signatures. Returns 0 if ctx is NULL.

See also

EpidMemberCreate

EpidWritePreSigs

size_t EpidGetSigSize

(

SigRl const *

sig_rl

)

Computes the size in bytes required for a Intel(R) EPID signature.

Parameters

[in]

sig_rl

The signature based revocation list that is used. NULL is treated as a zero length list.

Returns

Size in bytes of an Intel(R) EPID signature including proofs for each entry in the signature based revocation list.

See also

SigRl

Examples:

signmsg.c.

bool EpidIsPrivKeyInGroup	(	GroupPubKey const *	pub_key,
		PrivKey const *	priv_key
	)

Tests if a member private key is valid without checking revocation.

Used to check that a member private key is a valid key for a group. This is useful as a cross check when creating a new member private key as part of the join process

Parameters

[in]	pub_key	The public key of the group.
[in]	priv_key	The private key to check.

Returns

bool

Return values

true	if the private key is valid for the group of the public key
false	if the private key is not valid for the group of the public key

See also

EpidRequestJoin

EpidStatus EpidMemberCreate	(	GroupPubKey const *	pub_key,
		PrivKey const *	priv_key,
		MemberPrecomp const *	precomp,
		BitSupplier	rnd_func,
		void *	rnd_param,
		MemberCtx **	ctx
	)

Creates a new member context.

Must be called to create the member context that is used by other "Member" APIs.

Allocates memory for the context, then initializes it.

EpidMemberDelete() must be called to safely release the member context.

Parameters

[in]	pub_key	The group certificate.
[in]	priv_key	The member private key.
[in]	precomp	Optional pre-computed data. If NULL the value is computed internally and is readable using EpidMemberWritePrecomp().
[in]	rnd_func	Random number generator.
[in]	rnd_param	Pass through context data for rnd_func.
[out]	ctx	Newly constructed member context.

Returns

EpidStatus

Warning

For security rnd_func should be a cryptographically secure random number generator.

Note

If the result is not kEpidNoErr the content of ctx is undefined.

See also

EpidMemberDelete

EpidMemberWritePrecomp

Examples:

signmsg.c.

void EpidMemberDelete

(

MemberCtx **

ctx

)

Deletes an existing member context.

Must be called to safely release a member context created using EpidMemberCreate().

De-initializes the context, frees memory used by the context, and sets the context pointer to NULL.

Parameters

[in,out]

ctx

The member context. Can be NULL.

See also

EpidMemberCreate

Examples:

signmsg.c.

EpidStatus EpidMemberSetHashAlg	(	MemberCtx *	ctx,
		HashAlg	hash_alg
	)

Sets the hash algorithm to be used by a member.

Parameters

[in]	ctx	The member context.
[in]	hash_alg	The hash algorithm to use.

Returns

EpidStatus

Note

If the result is not kEpidNoErr, the hash algorithm used by the member is undefined.

See also

EpidMemberCreate

HashAlg

Examples:

signmsg.c.

EpidStatus EpidMemberWritePrecomp	(	MemberCtx const *	ctx,
		MemberPrecomp *	precomp
	)

Serializes the pre-computed member settings.

Parameters

[in]	ctx	The member context.
[out]	precomp	The Serialized pre-computed member settings.

Returns

EpidStatus

Note

If the result is not kEpidNoErr, the content of precomp is undefined.

Examples:

signmsg.c.

EpidStatus EpidNrProve	(	MemberCtx const *	ctx,
		void const *	msg,
		size_t	msg_len,
		BasicSignature const *	sig,
		SigRlEntry const *	sigrl_entry,
		NrProof *	proof
	)

Calculates a non-revoked proof for a single signature based revocation list entry.

Used in constrained environments where, due to limited memory, it may not be possible to process through a large and potentially unbounded revocation list.

Parameters

[in]	ctx	The member context.
[in]	msg	The message.
[in]	msg_len	The length of message in bytes.
[in]	sig	The basic signature.
[in]	sigrl_entry	The signature based revocation list entry.
[out]	proof	The generated non-revoked proof.

Returns

EpidStatus

Note

This function should be used in conjunction with EpidSignBasic().

If the result is not kEpidNoErr, the content of proof is undefined.

See also

EpidMemberCreate

EpidSignBasic

EpidStatus EpidRegisterBaseName	(	MemberCtx *	ctx,
		void const *	basename,
		size_t	basename_len
	)

Registers a basename with a member.

To prevent loss of privacy, the member keeps a list of basenames (corresponding to authorized verifiers). The member signs a message with a basename only if the basename is in the member's basename list.

Warning

The use of a name-based signature creates a platform unique pseudonymous identifier. Because it reduces the member's privacy, the user should be notified when it is used and should have control over its use.

Parameters

[in]	ctx	The member context.
[in]	basename	The basename.
[in]	basename_len	Length of the basename.

Returns

EpidStatus

Return values

kEpidDuplicateErr

The basename was already registered.

Note

If the result is not kEpidNoErr or kEpidDuplicateErr it is undefined if the basename is registered.

Examples:

signmsg.c.

EpidStatus EpidRequestJoin	(	GroupPubKey const *	pub_key,
		IssuerNonce const *	ni,
		FpElemStr const *	f,
		BitSupplier	rnd_func,
		void *	rnd_param,
		HashAlg	hash_alg,
		JoinRequest *	join_request
	)

Creates a request to join a group.

The created request is part of the interaction with an issuer needed to join a group. This interaction with the issuer is outside the scope of this API.

Parameters

[in]	pub_key	The group certificate of group to join.
[in]	ni	The nonce chosen by issuer as part of join protocol.
[in]	f	A randomly selected integer in [1, p-1].
[in]	rnd_func	Random number generator.
[in]	rnd_param	Pass through context data for rnd_func.
[in]	hash_alg	The hash algorithm to be used.
[out]	join_request	The join request.

Returns

EpidStatus

Warning

For security rnd_func should be a cryptographically secure random number generator.

Note

The default hash algorithm in Member is SHA-512. This is the recommended option if you do not override the hash algorithm elsewhere.

If the result is not kEpidNoErr, the content of join_request is undefined.

See also

HashAlg

EpidStatus EpidSign	(	MemberCtx const *	ctx,
		void const *	msg,
		size_t	msg_len,
		void const *	basename,
		size_t	basename_len,
		SigRl const *	sig_rl,
		size_t	sig_rl_size,
		EpidSignature *	sig,
		size_t	sig_len
	)

Writes a Intel(R) EPID signature.

Parameters

[in]	ctx	The member context.
[in]	msg	The message to sign.
[in]	msg_len	The length in bytes of message.
[in]	basename	Optional basename. If basename is NULL a random basename is used. Signatures generated using random basenames are anonymous. Signatures generated using the same basename are linkable by the verifier. If a basename is provided, it must already be registered, or kEpidBadArgErr is returned.
[in]	basename_len	The size of basename in bytes. Must be 0 basename is NULL.
[in]	sig_rl	The signature based revocation list.
[in]	sig_rl_size	The size in bytes of the signature based revocation list.
[out]	sig	The generated signature
[in]	sig_len	The size of signature in bytes. Must be equal to value returned by EpidGetSigSize().

Returns

EpidStatus

Note

If the result is not kEpidNoErr the content of sig is undefined.

See also

EpidMemberCreate

EpidMemberSetHashAlg

EpidGetSigSize

Examples:

signmsg.c.

EpidStatus EpidSignBasic	(	MemberCtx const *	ctx,
		void const *	msg,
		size_t	msg_len,
		void const *	basename,
		size_t	basename_len,
		BasicSignature *	sig
	)

Creates a basic signature for use in constrained environment.

Used in constrained environments where, due to limited memory, it may not be possible to process through a large and potentially unbounded revocation list.

Parameters

[in]	ctx	The member context.
[in]	msg	The message.
[in]	msg_len	The length of message in bytes.
[in]	basename	Optional basename. If basename is NULL a random basename is used. Signatures generated using random basenames are anonymous. Signatures generated using the same basename are linkable by the verifier. If a basename is provided it must already be registered or kEpidBadArgErr is returned.
[in]	basename_len	The size of basename in bytes. Must be 0 basename is NULL.
[out]	sig	The generated basic signature

Returns

EpidStatus

Note

This function should be used in conjunction with EpidNrProve()

If the result is not kEpidNoErr the content of sig, is undefined.

See also

EpidMemberCreate

EpidNrProve

EpidStatus EpidWritePreSigs	(	MemberCtx *	ctx,
		PreComputedSignature *	presigs,
		size_t	number_presigs
	)

Serializes pre-computed signatures from the member's pool.

Removes requested number of pre-computed signatures from member's pool and stores them in presigs array. Use EpidAddPreSigs to add pre-computed signatures to the pool.

Parameters

[in]	ctx	The member context.
[out]	presigs	An existing buffer of pre-computed signatures.
[in]	number_presigs	Number of pre-computed signatures to read. Number_presigs must not be greater than the value returned by EpidGetNumPreSigs.

Returns

EpidStatus

Note

If the result is not kEpidNoErr the state of the pre-computed signature pool, and of presigs, is undefined.

See also

EpidMemberCreate

EpidGetNumPreSigs

EpidAddPreSigs