crypto/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_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_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_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);

  // 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