crypto/trust_token/internal.h - boringssl - Git at Google

 /* Copyright (c) 2019, Google Inc.
  *
  * Permission to use, copy, modify, and/or distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
  * copyright notice and this permission notice appear in all copies.
  *
  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
  * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

 #ifndef OPENSSL_HEADER_TRUST_TOKEN_INTERNAL_H
 #define OPENSSL_HEADER_TRUST_TOKEN_INTERNAL_H

 #include <openssl/base.h>
 #include <openssl/ec.h>
 #include <openssl/ec_key.h>
 #include <openssl/nid.h>

 #include "../fipsmodule/ec/internal.h"

 #include <openssl/trust_token.h>


 #if defined(__cplusplus)
 extern "C" {
 #endif


 // For the following cryptographic schemes, we use P-384 instead of our usual
 // choice of P-256. See Appendix I of
 // https://eprint.iacr.org/2020/072/20200324:214215 which describes two attacks
 // which may affect smaller curves. In particular, p-1 for P-256 is smooth,
 // giving a low complexity for the p-1 attack. P-384's p-1 has a 281-bit prime
 // factor,
 // 3055465788140352002733946906144561090641249606160407884365391979704929268480326390471.
 // This lower-bounds the p-1 attack at O(2^140). The p+1 attack is lower-bounded
 // by O(p^(1/3)) or O(2^128), so we do not need to check the smoothness of p+1.


 // TRUST_TOKEN_NONCE_SIZE is the size of nonces used as part of the Trust_Token
 // protocol.
 #define TRUST_TOKEN_NONCE_SIZE 64

 typedef struct {
   // TODO(https://crbug.com/boringssl/334): These should store |EC_PRECOMP| so
   // that |TRUST_TOKEN_finish_issuance| can use |ec_point_mul_scalar_precomp|.
   EC_AFFINE pub0;
   EC_AFFINE pub1;
   EC_AFFINE pubs;
 } TRUST_TOKEN_CLIENT_KEY;

 typedef struct {
   EC_SCALAR x0;
   EC_SCALAR y0;
   EC_SCALAR x1;
   EC_SCALAR y1;
   EC_SCALAR xs;
   EC_SCALAR ys;
   EC_AFFINE pub0;
   EC_PRECOMP pub0_precomp;
   EC_AFFINE pub1;
   EC_PRECOMP pub1_precomp;
   EC_AFFINE pubs;
   EC_PRECOMP pubs_precomp;
 } TRUST_TOKEN_ISSUER_KEY;

 // TRUST_TOKEN_PRETOKEN represents the intermediate state a client keeps during
 // a Trust_Token issuance operation.
 typedef struct pmb_pretoken_st {
   uint8_t t[TRUST_TOKEN_NONCE_SIZE];
   EC_SCALAR r;
   EC_AFFINE Tp;
 } TRUST_TOKEN_PRETOKEN;

 // TRUST_TOKEN_PRETOKEN_free releases the memory associated with |token|.
 OPENSSL_EXPORT void TRUST_TOKEN_PRETOKEN_free(TRUST_TOKEN_PRETOKEN *token);

 DEFINE_STACK_OF(TRUST_TOKEN_PRETOKEN)


 // PMBTokens.
 //
 // PMBTokens is described in https://eprint.iacr.org/2020/072/20200324:214215
 // and provides anonymous tokens with private metadata. We implement the
 // construction with validity verification, described in appendix H,
 // construction 6.

 // The following functions implement the corresponding |TRUST_TOKENS_METHOD|
 // functions for |TRUST_TOKENS_experiment_v1|'s PMBTokens construction which
 // uses P-384.
 int pmbtoken_exp1_generate_key(CBB *out_private, CBB *out_public);
 int pmbtoken_exp1_derive_key_from_secret(CBB *out_private, CBB *out_public,
                                          const uint8_t *secret,
                                          size_t secret_len);
 int pmbtoken_exp1_client_key_from_bytes(TRUST_TOKEN_CLIENT_KEY *key,
                                         const uint8_t *in, size_t len);
 int pmbtoken_exp1_issuer_key_from_bytes(TRUST_TOKEN_ISSUER_KEY *key,
                                         const uint8_t *in, size_t len);
 STACK_OF(TRUST_TOKEN_PRETOKEN) * pmbtoken_exp1_blind(CBB *cbb, size_t count);
 int pmbtoken_exp1_sign(const TRUST_TOKEN_ISSUER_KEY *key, CBB *cbb, CBS *cbs,
                        size_t num_requested, size_t num_to_issue,
                        uint8_t private_metadata);
 STACK_OF(TRUST_TOKEN) *
     pmbtoken_exp1_unblind(const TRUST_TOKEN_CLIENT_KEY *key,
                           const STACK_OF(TRUST_TOKEN_PRETOKEN) * pretokens,
                           CBS *cbs, size_t count, uint32_t key_id);
 int pmbtoken_exp1_read(const TRUST_TOKEN_ISSUER_KEY *key,
                        uint8_t out_nonce[TRUST_TOKEN_NONCE_SIZE],
                        uint8_t *out_private_metadata, const uint8_t *token,
                        size_t token_len);

 // pmbtoken_exp1_get_h_for_testing returns H in uncompressed coordinates. This
 // function is used to confirm H was computed as expected.
 OPENSSL_EXPORT int pmbtoken_exp1_get_h_for_testing(uint8_t out[97]);

 // The following functions implement the corresponding |TRUST_TOKENS_METHOD|
 // functions for |TRUST_TOKENS_experiment_v2|'s PMBTokens construction which
 // uses P-384.
 int pmbtoken_exp2_generate_key(CBB *out_private, CBB *out_public);
 int pmbtoken_exp2_derive_key_from_secret(CBB *out_private, CBB *out_public,
                                          const uint8_t *secret,
                                          size_t secret_len);
 int pmbtoken_exp2_client_key_from_bytes(TRUST_TOKEN_CLIENT_KEY *key,
                                         const uint8_t *in, size_t len);
 int pmbtoken_exp2_issuer_key_from_bytes(TRUST_TOKEN_ISSUER_KEY *key,
                                         const uint8_t *in, size_t len);
 STACK_OF(TRUST_TOKEN_PRETOKEN) * pmbtoken_exp2_blind(CBB *cbb, size_t count);
 int pmbtoken_exp2_sign(const TRUST_TOKEN_ISSUER_KEY *key, CBB *cbb, CBS *cbs,
                        size_t num_requested, size_t num_to_issue,
                        uint8_t private_metadata);
 STACK_OF(TRUST_TOKEN) *
     pmbtoken_exp2_unblind(const TRUST_TOKEN_CLIENT_KEY *key,
                           const STACK_OF(TRUST_TOKEN_PRETOKEN) * pretokens,
                           CBS *cbs, size_t count, uint32_t key_id);
 int pmbtoken_exp2_read(const TRUST_TOKEN_ISSUER_KEY *key,
                        uint8_t out_nonce[TRUST_TOKEN_NONCE_SIZE],
                        uint8_t *out_private_metadata, const uint8_t *token,
                        size_t token_len);

 // pmbtoken_exp2_get_h_for_testing returns H in uncompressed coordinates. This
 // function is used to confirm H was computed as expected.
 OPENSSL_EXPORT int pmbtoken_exp2_get_h_for_testing(uint8_t out[97]);


 // VOPRF.
 //
 // VOPRFs are described in https://tools.ietf.org/html/draft-irtf-cfrg-voprf-04
 // and provide anonymous tokens. This implementation uses TrustToken DSTs and
 // the DLEQ batching primitive from
 // https://eprint.iacr.org/2020/072/20200324:214215.
 // VOPRF only uses the |pub|' field of the TRUST_TOKEN_CLIENT_KEY and
 // |xs|/|pubs| fields of the TRUST_TOKEN_ISSUER_KEY.

 // The following functions implement the corresponding |TRUST_TOKENS_METHOD|
 // functions for |TRUST_TOKENS_experiment_v2|'s VOPRF construction which uses
 // P-384.
 int voprf_exp2_generate_key(CBB *out_private, CBB *out_public);
 int voprf_exp2_derive_key_from_secret(CBB *out_private, CBB *out_public,
                                       const uint8_t *secret, size_t secret_len);
 int voprf_exp2_client_key_from_bytes(TRUST_TOKEN_CLIENT_KEY *key,
                                      const uint8_t *in, size_t len);
 int voprf_exp2_issuer_key_from_bytes(TRUST_TOKEN_ISSUER_KEY *key,
                                      const uint8_t *in, size_t len);
 STACK_OF(TRUST_TOKEN_PRETOKEN) * voprf_exp2_blind(CBB *cbb, size_t count);
 int voprf_exp2_sign(const TRUST_TOKEN_ISSUER_KEY *key, CBB *cbb, CBS *cbs,
                     size_t num_requested, size_t num_to_issue,
                     uint8_t private_metadata);
 STACK_OF(TRUST_TOKEN) *
     voprf_exp2_unblind(const TRUST_TOKEN_CLIENT_KEY *key,
                        const STACK_OF(TRUST_TOKEN_PRETOKEN) * pretokens,
                        CBS *cbs, size_t count, uint32_t key_id);
 int voprf_exp2_read(const TRUST_TOKEN_ISSUER_KEY *key,
                     uint8_t out_nonce[TRUST_TOKEN_NONCE_SIZE],
                     uint8_t *out_private_metadata, const uint8_t *token,
                     size_t token_len);


 // Trust Tokens internals.

 struct trust_token_method_st {
   // generate_key generates a fresh keypair and writes their serialized
   // forms into |out_private| and |out_public|. It returns one on success and
   // zero on failure.
   int (*generate_key)(CBB *out_private, CBB *out_public);

   // derive_key_from_secret deterministically derives a keypair based on
   // |secret| and writes their serialized forms into |out_private| and
   // |out_public|. It returns one on success and zero on failure.
   int (*derive_key_from_secret)(CBB *out_private, CBB *out_public,
                                   const uint8_t *secret, size_t secret_len);

   // client_key_from_bytes decodes a client key from |in| and sets |key|
   // to the resulting key. It returns one on success and zero
   // on failure.
   int (*client_key_from_bytes)(TRUST_TOKEN_CLIENT_KEY *key, const uint8_t *in,
                                size_t len);

   // issuer_key_from_bytes decodes a issuer key from |in| and sets |key|
   // to the resulting key. It returns one on success and zero
   // on failure.
   int (*issuer_key_from_bytes)(TRUST_TOKEN_ISSUER_KEY *key, const uint8_t *in,
                                size_t len);

   // blind generates a new issuance request for |count| tokens. On
   // success, it returns a newly-allocated |STACK_OF(TRUST_TOKEN_PRETOKEN)| and
   // writes a request to the issuer to |cbb|. On failure, it returns NULL. The
   // |STACK_OF(TRUST_TOKEN_PRETOKEN)|s should be passed to |pmbtoken_unblind| when
   // the server responds.
   //
   // This function implements the AT.Usr0 operation.
   STACK_OF(TRUST_TOKEN_PRETOKEN) * (*blind)(CBB *cbb, size_t count);

   // sign parses a request for |num_requested| tokens from |cbs| and
   // issues |num_to_issue| tokens with |key| and a private metadata value of
   // |private_metadata|. It then writes the response to |cbb|. It returns one on
   // success and zero on failure.
   //
   // This function implements the AT.Sig operation.
   int (*sign)(const TRUST_TOKEN_ISSUER_KEY *key, CBB *cbb, CBS *cbs,
               size_t num_requested, size_t num_to_issue,
               uint8_t private_metadata);

   // unblind processes an issuance response for |count| tokens from |cbs|
   // and unblinds the signed tokens. |pretokens| are the pre-tokens returned
   // from the corresponding |blind| call. On success, the function returns a
   // newly-allocated |STACK_OF(TRUST_TOKEN)| containing the resulting tokens.
   // Each token's serialization will have |key_id| prepended. Otherwise, it
   // returns NULL.
   //
   // This function implements the AT.Usr1 operation.
   STACK_OF(TRUST_TOKEN) *
       (*unblind)(const TRUST_TOKEN_CLIENT_KEY *key,
                  const STACK_OF(TRUST_TOKEN_PRETOKEN) * pretokens, CBS *cbs,
                  size_t count, uint32_t key_id);

   // read parses a PMBToken from |token| and verifies it using |key|. On
   // success, it returns one and stores the nonce and private metadata bit in
   // |out_nonce| and |*out_private_metadata|. Otherwise, it returns zero. Note
   // that, unlike the output of |unblind|, |token| does not have a
   // four-byte key ID prepended.
   int (*read)(const TRUST_TOKEN_ISSUER_KEY *key,
               uint8_t out_nonce[TRUST_TOKEN_NONCE_SIZE],
               uint8_t *out_private_metadata, const uint8_t *token,
               size_t token_len);

   // whether the construction supports private metadata.
   int has_private_metadata;

   // max keys that can be configured.
   size_t max_keys;

   // whether the SRR is part of the protocol.
   int has_srr;
 };

 // Structure representing a single Trust Token public key with the specified ID.
 struct trust_token_client_key_st {
   uint32_t id;
   TRUST_TOKEN_CLIENT_KEY key;
 };

 // Structure representing a single Trust Token private key with the specified
 // ID.
 struct trust_token_issuer_key_st {
   uint32_t id;
   TRUST_TOKEN_ISSUER_KEY key;
 };

 struct trust_token_client_st {
   const TRUST_TOKEN_METHOD *method;

   // max_batchsize is the maximum supported batchsize.
   uint16_t max_batchsize;

   // keys is the set of public keys that are supported by the client for
   // issuance/redemptions.
   struct trust_token_client_key_st keys[6];

   // num_keys is the number of keys currently configured.
   size_t num_keys;

   // pretokens is the intermediate state during an active issuance.
   STACK_OF(TRUST_TOKEN_PRETOKEN)* pretokens;

   // srr_key is the public key used to verify the signature of the SRR.
   EVP_PKEY *srr_key;
 };


 struct trust_token_issuer_st {
   const TRUST_TOKEN_METHOD *method;

   // max_batchsize is the maximum supported batchsize.
   uint16_t max_batchsize;

   // keys is the set of private keys that are supported by the issuer for
   // issuance/redemptions. The public metadata is an index into this list of
   // keys.
   struct trust_token_issuer_key_st keys[6];

   // num_keys is the number of keys currently configured.
   size_t num_keys;

   // srr_key is the private key used to sign the SRR.
   EVP_PKEY *srr_key;

   // metadata_key is the secret material used to encode the private metadata bit
   // in the SRR.
   uint8_t *metadata_key;
   size_t metadata_key_len;
 };


 #if defined(__cplusplus)
 }  // extern C

 extern "C++" {

 BSSL_NAMESPACE_BEGIN

 BORINGSSL_MAKE_DELETER(TRUST_TOKEN_PRETOKEN, TRUST_TOKEN_PRETOKEN_free)

 BSSL_NAMESPACE_END

 }  // extern C++
 #endif

 #endif  // OPENSSL_HEADER_TRUST_TOKEN_INTERNAL_H
	/* Copyright (c) 2019, Google Inc.
	*
	* Permission to use, copy, modify, and/or distribute this software for any
	* purpose with or without fee is hereby granted, provided that the above
	* copyright notice and this permission notice appear in all copies.
	*
	* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
	* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
	* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
	* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
	* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
	* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
	* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

	#ifndef OPENSSL_HEADER_TRUST_TOKEN_INTERNAL_H
	#define OPENSSL_HEADER_TRUST_TOKEN_INTERNAL_H

	#include <openssl/base.h>
	#include <openssl/ec.h>
	#include <openssl/ec_key.h>
	#include <openssl/nid.h>

	#include "../fipsmodule/ec/internal.h"

	#include <openssl/trust_token.h>


	#if defined(__cplusplus)
	extern "C" {
	#endif


	// For the following cryptographic schemes, we use P-384 instead of our usual
	// choice of P-256. See Appendix I of
	// https://eprint.iacr.org/2020/072/20200324:214215 which describes two attacks
	// which may affect smaller curves. In particular, p-1 for P-256 is smooth,
	// giving a low complexity for the p-1 attack. P-384's p-1 has a 281-bit prime
	// factor,
	// 3055465788140352002733946906144561090641249606160407884365391979704929268480326390471.
	// This lower-bounds the p-1 attack at O(2^140). The p+1 attack is lower-bounded
	// by O(p^(1/3)) or O(2^128), so we do not need to check the smoothness of p+1.


	// TRUST_TOKEN_NONCE_SIZE is the size of nonces used as part of the Trust_Token
	// protocol.
	#define TRUST_TOKEN_NONCE_SIZE 64

	typedef struct {
	// TODO(https://crbug.com/boringssl/334): These should store \|EC_PRECOMP\| so
	// that \|TRUST_TOKEN_finish_issuance\| can use \|ec_point_mul_scalar_precomp\|.
	EC_AFFINE pub0;
	EC_AFFINE pub1;
	EC_AFFINE pubs;
	} TRUST_TOKEN_CLIENT_KEY;

	typedef struct {
	EC_SCALAR x0;
	EC_SCALAR y0;
	EC_SCALAR x1;
	EC_SCALAR y1;
	EC_SCALAR xs;
	EC_SCALAR ys;
	EC_AFFINE pub0;
	EC_PRECOMP pub0_precomp;
	EC_AFFINE pub1;
	EC_PRECOMP pub1_precomp;
	EC_AFFINE pubs;
	EC_PRECOMP pubs_precomp;
	} TRUST_TOKEN_ISSUER_KEY;

	// TRUST_TOKEN_PRETOKEN represents the intermediate state a client keeps during
	// a Trust_Token issuance operation.
	typedef struct pmb_pretoken_st {
	uint8_t t[TRUST_TOKEN_NONCE_SIZE];
	EC_SCALAR r;
	EC_AFFINE Tp;
	} TRUST_TOKEN_PRETOKEN;

	// TRUST_TOKEN_PRETOKEN_free releases the memory associated with \|token\|.
	OPENSSL_EXPORT void TRUST_TOKEN_PRETOKEN_free(TRUST_TOKEN_PRETOKEN *token);

	DEFINE_STACK_OF(TRUST_TOKEN_PRETOKEN)


	// PMBTokens.
	//
	// PMBTokens is described in https://eprint.iacr.org/2020/072/20200324:214215
	// and provides anonymous tokens with private metadata. We implement the
	// construction with validity verification, described in appendix H,
	// construction 6.

	// The following functions implement the corresponding \|TRUST_TOKENS_METHOD\|
	// functions for \|TRUST_TOKENS_experiment_v1\|'s PMBTokens construction which
	// uses P-384.
	int pmbtoken_exp1_generate_key(CBB out_private, CBB out_public);
	int pmbtoken_exp1_derive_key_from_secret(CBB out_private, CBB out_public,
	const uint8_t *secret,
	size_t secret_len);
	int pmbtoken_exp1_client_key_from_bytes(TRUST_TOKEN_CLIENT_KEY *key,
	const uint8_t *in, size_t len);
	int pmbtoken_exp1_issuer_key_from_bytes(TRUST_TOKEN_ISSUER_KEY *key,
	const uint8_t *in, size_t len);
	STACK_OF(TRUST_TOKEN_PRETOKEN) * pmbtoken_exp1_blind(CBB *cbb, size_t count);
	int pmbtoken_exp1_sign(const TRUST_TOKEN_ISSUER_KEY key, CBB cbb, CBS *cbs,
	size_t num_requested, size_t num_to_issue,
	uint8_t private_metadata);
	STACK_OF(TRUST_TOKEN) *
	pmbtoken_exp1_unblind(const TRUST_TOKEN_CLIENT_KEY *key,
	const STACK_OF(TRUST_TOKEN_PRETOKEN) * pretokens,
	CBS *cbs, size_t count, uint32_t key_id);
	int pmbtoken_exp1_read(const TRUST_TOKEN_ISSUER_KEY *key,
	uint8_t out_nonce[TRUST_TOKEN_NONCE_SIZE],
	uint8_t out_private_metadata, const uint8_t token,
	size_t token_len);

	// pmbtoken_exp1_get_h_for_testing returns H in uncompressed coordinates. This
	// function is used to confirm H was computed as expected.
	OPENSSL_EXPORT int pmbtoken_exp1_get_h_for_testing(uint8_t out[97]);

	// The following functions implement the corresponding \|TRUST_TOKENS_METHOD\|
	// functions for \|TRUST_TOKENS_experiment_v2\|'s PMBTokens construction which
	// uses P-384.
	int pmbtoken_exp2_generate_key(CBB out_private, CBB out_public);
	int pmbtoken_exp2_derive_key_from_secret(CBB out_private, CBB out_public,
	const uint8_t *secret,
	size_t secret_len);
	int pmbtoken_exp2_client_key_from_bytes(TRUST_TOKEN_CLIENT_KEY *key,
	const uint8_t *in, size_t len);
	int pmbtoken_exp2_issuer_key_from_bytes(TRUST_TOKEN_ISSUER_KEY *key,
	const uint8_t *in, size_t len);
	STACK_OF(TRUST_TOKEN_PRETOKEN) * pmbtoken_exp2_blind(CBB *cbb, size_t count);
	int pmbtoken_exp2_sign(const TRUST_TOKEN_ISSUER_KEY key, CBB cbb, CBS *cbs,
	size_t num_requested, size_t num_to_issue,
	uint8_t private_metadata);
	STACK_OF(TRUST_TOKEN) *
	pmbtoken_exp2_unblind(const TRUST_TOKEN_CLIENT_KEY *key,
	const STACK_OF(TRUST_TOKEN_PRETOKEN) * pretokens,
	CBS *cbs, size_t count, uint32_t key_id);
	int pmbtoken_exp2_read(const TRUST_TOKEN_ISSUER_KEY *key,
	uint8_t out_nonce[TRUST_TOKEN_NONCE_SIZE],
	uint8_t out_private_metadata, const uint8_t token,
	size_t token_len);

	// pmbtoken_exp2_get_h_for_testing returns H in uncompressed coordinates. This
	// function is used to confirm H was computed as expected.
	OPENSSL_EXPORT int pmbtoken_exp2_get_h_for_testing(uint8_t out[97]);


	// VOPRF.
	//
	// VOPRFs are described in https://tools.ietf.org/html/draft-irtf-cfrg-voprf-04
	// and provide anonymous tokens. This implementation uses TrustToken DSTs and
	// the DLEQ batching primitive from
	// https://eprint.iacr.org/2020/072/20200324:214215.
	// VOPRF only uses the \|pub\|' field of the TRUST_TOKEN_CLIENT_KEY and
	// \|xs\|/\|pubs\| fields of the TRUST_TOKEN_ISSUER_KEY.

	// The following functions implement the corresponding \|TRUST_TOKENS_METHOD\|
	// functions for \|TRUST_TOKENS_experiment_v2\|'s VOPRF construction which uses
	// P-384.
	int voprf_exp2_generate_key(CBB out_private, CBB out_public);
	int voprf_exp2_derive_key_from_secret(CBB out_private, CBB out_public,
	const uint8_t *secret, size_t secret_len);
	int voprf_exp2_client_key_from_bytes(TRUST_TOKEN_CLIENT_KEY *key,
	const uint8_t *in, size_t len);
	int voprf_exp2_issuer_key_from_bytes(TRUST_TOKEN_ISSUER_KEY *key,
	const uint8_t *in, size_t len);
	STACK_OF(TRUST_TOKEN_PRETOKEN) * voprf_exp2_blind(CBB *cbb, size_t count);
	int voprf_exp2_sign(const TRUST_TOKEN_ISSUER_KEY key, CBB cbb, CBS *cbs,
	size_t num_requested, size_t num_to_issue,
	uint8_t private_metadata);
	STACK_OF(TRUST_TOKEN) *
	voprf_exp2_unblind(const TRUST_TOKEN_CLIENT_KEY *key,
	const STACK_OF(TRUST_TOKEN_PRETOKEN) * pretokens,
	CBS *cbs, size_t count, uint32_t key_id);
	int voprf_exp2_read(const TRUST_TOKEN_ISSUER_KEY *key,
	uint8_t out_nonce[TRUST_TOKEN_NONCE_SIZE],
	uint8_t out_private_metadata, const uint8_t token,
	size_t token_len);


	// Trust Tokens internals.

	struct trust_token_method_st {
	// generate_key generates a fresh keypair and writes their serialized
	// forms into \|out_private\| and \|out_public\|. It returns one on success and
	// zero on failure.
	int (generate_key)(CBB out_private, CBB *out_public);

	// derive_key_from_secret deterministically derives a keypair based on
	// \|secret\| and writes their serialized forms into \|out_private\| and
	// \|out_public\|. It returns one on success and zero on failure.
	int (derive_key_from_secret)(CBB out_private, CBB *out_public,
	const uint8_t *secret, size_t secret_len);

	// client_key_from_bytes decodes a client key from \|in\| and sets \|key\|
	// to the resulting key. It returns one on success and zero
	// on failure.
	int (client_key_from_bytes)(TRUST_TOKEN_CLIENT_KEY key, const uint8_t *in,
	size_t len);

	// issuer_key_from_bytes decodes a issuer key from \|in\| and sets \|key\|
	// to the resulting key. It returns one on success and zero
	// on failure.
	int (issuer_key_from_bytes)(TRUST_TOKEN_ISSUER_KEY key, const uint8_t *in,
	size_t len);

	// blind generates a new issuance request for \|count\| tokens. On
	// success, it returns a newly-allocated \|STACK_OF(TRUST_TOKEN_PRETOKEN)\| and
	// writes a request to the issuer to \|cbb\|. On failure, it returns NULL. The
	// \|STACK_OF(TRUST_TOKEN_PRETOKEN)\|s should be passed to \|pmbtoken_unblind\| when
	// the server responds.
	//
	// This function implements the AT.Usr0 operation.
	STACK_OF(TRUST_TOKEN_PRETOKEN) * (blind)(CBB cbb, size_t count);

	// sign parses a request for \|num_requested\| tokens from \|cbs\| and
	// issues \|num_to_issue\| tokens with \|key\| and a private metadata value of
	// \|private_metadata\|. It then writes the response to \|cbb\|. It returns one on
	// success and zero on failure.
	//
	// This function implements the AT.Sig operation.
	int (sign)(const TRUST_TOKEN_ISSUER_KEY key, CBB cbb, CBS cbs,
	size_t num_requested, size_t num_to_issue,
	uint8_t private_metadata);

	// unblind processes an issuance response for \|count\| tokens from \|cbs\|
	// and unblinds the signed tokens. \|pretokens\| are the pre-tokens returned
	// from the corresponding \|blind\| call. On success, the function returns a
	// newly-allocated \|STACK_OF(TRUST_TOKEN)\| containing the resulting tokens.
	// Each token's serialization will have \|key_id\| prepended. Otherwise, it
	// returns NULL.
	//
	// This function implements the AT.Usr1 operation.
	STACK_OF(TRUST_TOKEN) *
	(unblind)(const TRUST_TOKEN_CLIENT_KEY key,
	const STACK_OF(TRUST_TOKEN_PRETOKEN) * pretokens, CBS *cbs,
	size_t count, uint32_t key_id);

	// read parses a PMBToken from \|token\| and verifies it using \|key\|. On
	// success, it returns one and stores the nonce and private metadata bit in
	// \|out_nonce\| and \|*out_private_metadata\|. Otherwise, it returns zero. Note
	// that, unlike the output of \|unblind\|, \|token\| does not have a
	// four-byte key ID prepended.
	int (read)(const TRUST_TOKEN_ISSUER_KEY key,
	uint8_t out_nonce[TRUST_TOKEN_NONCE_SIZE],
	uint8_t out_private_metadata, const uint8_t token,
	size_t token_len);

	// whether the construction supports private metadata.
	int has_private_metadata;

	// max keys that can be configured.
	size_t max_keys;

	// whether the SRR is part of the protocol.
	int has_srr;
	};

	// Structure representing a single Trust Token public key with the specified ID.
	struct trust_token_client_key_st {
	uint32_t id;
	TRUST_TOKEN_CLIENT_KEY key;
	};

	// Structure representing a single Trust Token private key with the specified
	// ID.
	struct trust_token_issuer_key_st {
	uint32_t id;
	TRUST_TOKEN_ISSUER_KEY key;
	};

	struct trust_token_client_st {
	const TRUST_TOKEN_METHOD *method;

	// max_batchsize is the maximum supported batchsize.
	uint16_t max_batchsize;

	// keys is the set of public keys that are supported by the client for
	// issuance/redemptions.
	struct trust_token_client_key_st keys[6];

	// num_keys is the number of keys currently configured.
	size_t num_keys;

	// pretokens is the intermediate state during an active issuance.
	STACK_OF(TRUST_TOKEN_PRETOKEN)* pretokens;

	// srr_key is the public key used to verify the signature of the SRR.
	EVP_PKEY *srr_key;
	};


	struct trust_token_issuer_st {
	const TRUST_TOKEN_METHOD *method;

	// max_batchsize is the maximum supported batchsize.
	uint16_t max_batchsize;

	// keys is the set of private keys that are supported by the issuer for
	// issuance/redemptions. The public metadata is an index into this list of
	// keys.
	struct trust_token_issuer_key_st keys[6];

	// num_keys is the number of keys currently configured.
	size_t num_keys;

	// srr_key is the private key used to sign the SRR.
	EVP_PKEY *srr_key;

	// metadata_key is the secret material used to encode the private metadata bit
	// in the SRR.
	uint8_t *metadata_key;
	size_t metadata_key_len;
	};


	#if defined(__cplusplus)
	} // extern C

	extern "C++" {

	BSSL_NAMESPACE_BEGIN

	BORINGSSL_MAKE_DELETER(TRUST_TOKEN_PRETOKEN, TRUST_TOKEN_PRETOKEN_free)

	BSSL_NAMESPACE_END

	} // extern C++
	#endif

	#endif // OPENSSL_HEADER_TRUST_TOKEN_INTERNAL_H