lighttpd1.4/src/mod_auth.c

#include "first.h"

#include <stdlib.h>
#include <string.h>

#include "sys-crypto-md.h" /* USE_LIB_CRYPTO */

#include "base.h"
#include "plugin.h"
#include "http_auth.h"
#include "http_header.h"
#include "log.h"

/**
 * auth framework
 */

typedef struct {
    const http_auth_backend_t *auth_backend;
    const array *auth_require;
    unsigned int auth_extern_authn;
} plugin_config;

typedef struct {
    PLUGIN_DATA;
    plugin_config defaults;
    plugin_config conf;
} plugin_data;

static handler_t mod_auth_check_basic(request_st *r, void *p_d, const struct http_auth_require_t *require, const struct http_auth_backend_t *backend);
static handler_t mod_auth_check_digest(request_st *r, void *p_d, const struct http_auth_require_t *require, const struct http_auth_backend_t *backend);
static handler_t mod_auth_check_extern(request_st *r, void *p_d, const struct http_auth_require_t *require, const struct http_auth_backend_t *backend);

INIT_FUNC(mod_auth_init) {
	static const http_auth_scheme_t http_auth_scheme_basic  = { "basic",  mod_auth_check_basic,  NULL };
	static const http_auth_scheme_t http_auth_scheme_digest = { "digest", mod_auth_check_digest, NULL };
	static const http_auth_scheme_t http_auth_scheme_extern = { "extern", mod_auth_check_extern, NULL };
	plugin_data *p;

	/* register http_auth_scheme_* */
	http_auth_scheme_set(&http_auth_scheme_basic);
	http_auth_scheme_set(&http_auth_scheme_digest);
	http_auth_scheme_set(&http_auth_scheme_extern);

	p = calloc(1, sizeof(*p));

	return p;
}

FREE_FUNC(mod_auth_free) {
    plugin_data * const p = p_d;
    if (NULL == p->cvlist) return;
    /* (init i to 0 if global context; to 1 to skip empty global context) */
    for (int i = !p->cvlist[0].v.u2[1], used = p->nconfig; i < used; ++i) {
        config_plugin_value_t *cpv = p->cvlist + p->cvlist[i].v.u2[0];
        for (; -1 != cpv->k_id; ++cpv) {
            if (cpv->vtype != T_CONFIG_LOCAL || NULL == cpv->v.v) continue;
            switch (cpv->k_id) {
              case 1: /* auth.require */
                array_free(cpv->v.v);
                break;
              default:
                break;
            }
        }
    }
}

/* data type for mod_auth structured data
 * (parsed from auth.require array of strings) */
typedef struct {
    DATA_UNSET;
    http_auth_require_t *require;
} data_auth;

static void data_auth_free(data_unset *d)
{
    data_auth * const dauth = (data_auth *)d;
    free(dauth->key.ptr);
    http_auth_require_free(dauth->require);
    free(dauth);
}

static data_auth *data_auth_init(void)
{
    static const struct data_methods fn = {
      NULL, /* copy must not be called on this data */
      data_auth_free,
      NULL, /* insert_dup must not be called on this data */
      NULL  /* print must not be called on this data */
    };
    data_auth * const dauth = calloc(1, sizeof(*dauth));
    force_assert(NULL != dauth);
    dauth->type       = TYPE_OTHER;
    dauth->fn         = &fn;

    dauth->require = http_auth_require_init();

    return dauth;
}

static int mod_auth_algorithm_parse(http_auth_info_t *ai, const char *s) {
    size_t len;
    if (NULL == s) {
        ai->dalgo = HTTP_AUTH_DIGEST_MD5;
        ai->dlen  = HTTP_AUTH_DIGEST_MD5_BINLEN;
        return 1;
    }

    len = strlen(s);
    if (len > 5
        && (s[len-5]       ) == '-'
        && (s[len-4] | 0x20) == 's'
        && (s[len-3] | 0x20) == 'e'
        && (s[len-2] | 0x20) == 's'
        && (s[len-1] | 0x20) == 's') {
        ai->dalgo = HTTP_AUTH_DIGEST_SESS;
        len -= 5;
    }
    else {
        ai->dalgo = HTTP_AUTH_DIGEST_NONE;
    }

    if (3 == len
        && 'm' == (s[0] | 0x20)
        && 'd' == (s[1] | 0x20)
        && '5' == (s[2]       )) {
        ai->dalgo |= HTTP_AUTH_DIGEST_MD5;
        ai->dlen   = HTTP_AUTH_DIGEST_MD5_BINLEN;
        return 1;
    }
  #ifdef USE_LIB_CRYPTO
    else if (len >= 7
             && 's' == (s[0] | 0x20)
             && 'h' == (s[1] | 0x20)
             && 'a' == (s[2] | 0x20)
             && '-' == (s[3]       )) {
        if (len == 7 && s[4] == '2' && s[5] == '5' && s[6] == '6') {
            ai->dalgo |= HTTP_AUTH_DIGEST_SHA256;
            ai->dlen   = HTTP_AUTH_DIGEST_SHA256_BINLEN;
            return 1;
        }
      #ifdef USE_LIB_CRYPTO_SHA512_256
        if (len == 11 && 0 == memcmp(s+4, "512-256", 7)) {
            ai->dalgo |= HTTP_AUTH_DIGEST_SHA512_256;
            ai->dlen   = HTTP_AUTH_DIGEST_SHA512_256_BINLEN;
            return 1;
        }
      #endif
    }
  #endif
    return 0; /*(error)*/
}

static int mod_auth_algorithms_parse(int *algorithm, buffer *algos) {
    for (char *s = algos->ptr, *p; s; s = p ? p+1 : NULL) {
        http_auth_info_t ai;
        int rc;
        p = strchr(s, '|');
        if (p) *p = '\0';
        rc = mod_auth_algorithm_parse(&ai, s);
        if (p) *p = '|';
        if (!rc) return 0;
        *algorithm |= ai.dalgo;
    }
    return 1;
}

static int mod_auth_require_parse (http_auth_require_t * const require, const buffer *b, log_error_st *errh)
{
    /* user=name1|user=name2|group=name3|host=name4 */

    const char *str = b->ptr;
    const char *p;

    if (buffer_is_equal_string(b, CONST_STR_LEN("valid-user"))) {
        require->valid_user = 1;
        return 1; /* success */
    }

    do {
        const char *eq;
        size_t len;
        p = strchr(str, '|');
        len = NULL != p ? (size_t)(p - str) : strlen(str);
        eq = memchr(str, '=', len);
        if (NULL == eq) {
            log_error(errh, __FILE__, __LINE__,
              "error parsing auth.require 'require' field: missing '=' "
              "(expecting \"valid-user\" or \"user=a|user=b|group=g|host=h\"). "
              "error value: %s error near: %s", b->ptr, str);
            return 0;
        }
        if (eq[1] == '|' || eq[1] == '\0') {
            log_error(errh, __FILE__, __LINE__,
              "error parsing auth.require 'require' field: "
              "missing token after '=' "
              "(expecting \"valid-user\" or \"user=a|user=b|group=g|host=h\"). "
              "error value: %s error near: %s", b->ptr, str);
            return 0;
        }

        switch ((int)(eq - str)) {
          case 4:
            if (0 == memcmp(str, CONST_STR_LEN("user"))) {
                /*("user=" is 5)*/
                array_set_key_value(&require->user, str+5, len-5, CONST_STR_LEN(""));
                continue;
            }
            else if (0 == memcmp(str, CONST_STR_LEN("host"))) {
                /*("host=" is 5)*/
                array_set_key_value(&require->host, str+5, len-5, CONST_STR_LEN(""));
                log_error(errh, __FILE__, __LINE__,
                  "warning parsing auth.require 'require' field: "
                  "'host' not implemented; field value: %s", b->ptr);
                continue;
            }
            break; /* to error */
          case 5:
            if (0 == memcmp(str, CONST_STR_LEN("group"))) {
                /*("group=" is 6)*/
                array_set_key_value(&require->group, str+6, len-6, CONST_STR_LEN(""));
              #if 0/*(supported by mod_authn_ldap, but not all other backends)*/
                log_error(errh, __FILE__, __LINE__,
                  "warning parsing auth.require 'require' field: "
                  "'group' not implemented; field value: %s", b->ptr);
              #endif
                continue;
            }
            break; /* to error */
          case 10:
            if (0 == memcmp(str, CONST_STR_LEN("valid-user"))) {
                log_error(errh, __FILE__, __LINE__,
                  "error parsing auth.require 'require' field: "
                  "valid user can not be combined with other require rules "
                  "(expecting \"valid-user\" or "
                  "\"user=a|user=b|group=g|host=h\"). error value: %s", b->ptr);
                return 0;
            }
            break; /* to error */
          default:
            break; /* to error */
        }

        log_error(errh, __FILE__, __LINE__,
          "error parsing auth.require 'require' field: "
          "invalid/unsupported token "
          "(expecting \"valid-user\" or \"user=a|user=b|group=g|host=h\"). "
          "error value: %s error near: %s", b->ptr, str);
        return 0;

    } while (p && *((str = p+1)));

    return 1; /* success */
}

static handler_t mod_auth_require_parse_array(const array *value, array * const auth_require, log_error_st *errh)
{
		for (uint32_t n = 0; n < value->used; ++n) {
			size_t m;
			data_array *da_file = (data_array *)value->data[n];
			const buffer *method = NULL, *realm = NULL, *require = NULL;
			const buffer *nonce_secret = NULL;
			const http_auth_scheme_t *auth_scheme;
			buffer *algos = NULL;
			int algorithm = HTTP_AUTH_DIGEST_SESS;

			if (!array_is_kvstring(&da_file->value)) {
				log_error(errh, __FILE__, __LINE__,
				  "unexpected value for auth.require; expected "
				  "auth.require = ( \"urlpath\" => ( \"option\" => \"value\" ) )");

				return HANDLER_ERROR;
			}

			for (m = 0; m < da_file->value.used; m++) {
				if (da_file->value.data[m]->type == TYPE_STRING) {
					data_string *ds = (data_string *)da_file->value.data[m];
					if (buffer_is_equal_string(&ds->key, CONST_STR_LEN("method"))) {
						method = &ds->value;
					} else if (buffer_is_equal_string(&ds->key, CONST_STR_LEN("realm"))) {
						realm = &ds->value;
					} else if (buffer_is_equal_string(&ds->key, CONST_STR_LEN("require"))) {
						require = &ds->value;
					} else if (buffer_is_equal_string(&ds->key, CONST_STR_LEN("algorithm"))) {
						algos = &ds->value;
					} else if (buffer_is_equal_string(&ds->key, CONST_STR_LEN("nonce_secret"))) {
						nonce_secret = &ds->value;
					} else {
						log_error(errh, __FILE__, __LINE__,
						  "the field is unknown in: "
						  "auth.require = ( \"...\" => ( ..., -> \"%s\" <- => \"...\" ) )",
						  da_file->value.data[m]->key.ptr);

						return HANDLER_ERROR;
					}
				} else {
					log_error(errh, __FILE__, __LINE__,
					  "a string was expected for: "
					  "auth.require = ( \"...\" => ( ..., -> \"%s\" <- => \"...\" ) )",
					  da_file->value.data[m]->key.ptr);

					return HANDLER_ERROR;
				}
			}

			if (buffer_string_is_empty(method)) {
				log_error(errh, __FILE__, __LINE__,
				  "the method field is missing or blank in: "
				  "auth.require = ( \"...\" => ( ..., \"method\" => \"...\" ) )");
				return HANDLER_ERROR;
			} else {
				auth_scheme = http_auth_scheme_get(method);
				if (NULL == auth_scheme) {
					log_error(errh, __FILE__, __LINE__,
					  "unknown method %s (e.g. \"basic\", \"digest\" or \"extern\") in "
					  "auth.require = ( \"...\" => ( ..., \"method\" => \"...\") )", method->ptr);
					return HANDLER_ERROR;
				}
			}

			if (buffer_is_empty(realm)) {
				log_error(errh, __FILE__, __LINE__,
				  "the realm field is missing in: "
				  "auth.require = ( \"...\" => ( ..., \"realm\" => \"...\" ) )");
				return HANDLER_ERROR;
			}

			if (buffer_string_is_empty(require)) {
				log_error(errh, __FILE__, __LINE__,
				  "the require field is missing or blank in: "
				  "auth.require = ( \"...\" => ( ..., \"require\" => \"...\" ) )");
				return HANDLER_ERROR;
			}

			if (buffer_string_is_empty(algos)) {
				algorithm |= HTTP_AUTH_DIGEST_MD5;
			} else if (!mod_auth_algorithms_parse(&algorithm, algos)) {
				log_error(errh, __FILE__, __LINE__,
				  "invalid algorithm in: "
				  "auth.require = ( \"...\" => ( ..., \"algorithm\" => \"...\" ) )");
				return HANDLER_ERROR;
			}

			if (require) { /*(always true at this point)*/
				data_auth * const dauth = data_auth_init();
				buffer_copy_buffer(&dauth->key, &da_file->key);
				dauth->require->scheme = auth_scheme;
				dauth->require->algorithm = algorithm;
				dauth->require->realm = realm;
				dauth->require->nonce_secret = nonce_secret; /*(NULL is ok)*/
				if (!mod_auth_require_parse(dauth->require, require, errh)) {
					dauth->fn->free((data_unset *)dauth);
					return HANDLER_ERROR;
				}
				array_insert_unique(auth_require, (data_unset *)dauth);
			}
		}

	return HANDLER_GO_ON;
}

static void mod_auth_merge_config_cpv(plugin_config * const pconf, const config_plugin_value_t * const cpv) {
    switch (cpv->k_id) { /* index into static config_plugin_keys_t cpk[] */
      case 0: /* auth.backend */
        if (cpv->vtype == T_CONFIG_LOCAL)
            pconf->auth_backend = cpv->v.v;
        break;
      case 1: /* auth.require */
        if (cpv->vtype == T_CONFIG_LOCAL)
            pconf->auth_require = cpv->v.v;
        break;
      case 2: /* auth.extern-authn */
        pconf->auth_extern_authn = cpv->v.u;
      default:/* should not happen */
        return;
    }
}

static void mod_auth_merge_config(plugin_config * const pconf, const config_plugin_value_t *cpv) {
    do {
        mod_auth_merge_config_cpv(pconf, cpv);
    } while ((++cpv)->k_id != -1);
}

static void mod_auth_patch_config(request_st * const r, plugin_data * const p) {
    p->conf = p->defaults; /* copy small struct instead of memcpy() */
    /*memcpy(&p->conf, &p->defaults, sizeof(plugin_config));*/
    for (int i = 1, used = p->nconfig; i < used; ++i) {
        if (config_check_cond(r, (uint32_t)p->cvlist[i].k_id))
            mod_auth_merge_config(&p->conf, p->cvlist + p->cvlist[i].v.u2[0]);
    }
}

SETDEFAULTS_FUNC(mod_auth_set_defaults) {
    static const config_plugin_keys_t cpk[] = {
      { CONST_STR_LEN("auth.backend"),
        T_CONFIG_STRING,
        T_CONFIG_SCOPE_CONNECTION }
     ,{ CONST_STR_LEN("auth.require"),
        T_CONFIG_ARRAY_KVARRAY,
        T_CONFIG_SCOPE_CONNECTION }
     ,{ CONST_STR_LEN("auth.extern-authn"),
        T_CONFIG_BOOL,
        T_CONFIG_SCOPE_CONNECTION }
     ,{ NULL, 0,
        T_CONFIG_UNSET,
        T_CONFIG_SCOPE_UNSET }
    };

    plugin_data * const p = p_d;
    if (!config_plugin_values_init(srv, p, cpk, "mod_auth"))
        return HANDLER_ERROR;

    /* process and validate config directives
     * (init i to 0 if global context; to 1 to skip empty global context) */
    for (int i = !p->cvlist[0].v.u2[1]; i < p->nconfig; ++i) {
        config_plugin_value_t *cpv = p->cvlist + p->cvlist[i].v.u2[0];
        for (; -1 != cpv->k_id; ++cpv) {
            switch (cpv->k_id) {
              case 0: /* auth.backend */
                if (!buffer_string_is_empty(cpv->v.b)) {
                    const http_auth_backend_t * const auth_backend =
                      http_auth_backend_get(cpv->v.b);
                    if (NULL == auth_backend) {
                        log_error(srv->errh, __FILE__, __LINE__,
                          "auth.backend not supported: %s", cpv->v.b->ptr);
                        return HANDLER_ERROR;
                    }
                    *(const http_auth_backend_t **)&cpv->v.v = auth_backend;
                    cpv->vtype = T_CONFIG_LOCAL;
                }
                break;
              case 1: /* auth.require */
                {
                    array * const a = array_init(4);
                    if (HANDLER_GO_ON !=
                        mod_auth_require_parse_array(cpv->v.a, a, srv->errh)) {
                        array_free(a);
                        return HANDLER_ERROR;
                    }
                    cpv->v.a = a;
                    cpv->vtype = T_CONFIG_LOCAL;
                }
                break;
              case 2: /* auth.extern-authn */
                break;
              default:/* should not happen */
                break;
            }
        }
    }

    /* initialize p->defaults from global config context */
    if (p->nconfig > 0 && p->cvlist->v.u2[1]) {
        const config_plugin_value_t *cpv = p->cvlist + p->cvlist->v.u2[0];
        if (-1 != cpv->k_id)
            mod_auth_merge_config(&p->defaults, cpv);
    }

    return HANDLER_GO_ON;
}

static handler_t mod_auth_uri_handler(request_st * const r, void *p_d) {
	plugin_data *p = p_d;
	data_auth *dauth;

	mod_auth_patch_config(r, p);

	if (p->conf.auth_require == NULL) return HANDLER_GO_ON;

	/* search auth directives for first prefix match against URL path */
	/* if we have a case-insensitive FS we have to lower-case the URI here too */
	dauth = (!r->conf.force_lowercase_filenames)
	   ? (data_auth *)array_match_key_prefix(p->conf.auth_require, &r->uri.path)
	   : (data_auth *)array_match_key_prefix_nc(p->conf.auth_require, &r->uri.path);
	if (NULL == dauth) return HANDLER_GO_ON;

	{
			const http_auth_scheme_t * const scheme = dauth->require->scheme;
			if (p->conf.auth_extern_authn) {
				const buffer *vb = http_header_env_get(r, CONST_STR_LEN("REMOTE_USER"));
				if (NULL != vb && http_auth_match_rules(dauth->require, vb->ptr, NULL, NULL)) {
					return HANDLER_GO_ON;
				}
			}
			return scheme->checkfn(r, scheme->p_d, dauth->require, p->conf.auth_backend);
	}
}

int mod_auth_plugin_init(plugin *p);
int mod_auth_plugin_init(plugin *p) {
	p->version     = LIGHTTPD_VERSION_ID;
	p->name        = "auth";
	p->init        = mod_auth_init;
	p->set_defaults = mod_auth_set_defaults;
	p->handle_uri_clean = mod_auth_uri_handler;
	p->cleanup     = mod_auth_free;

	return 0;
}




/*
 * auth schemes (basic, digest, extern)
 *
 * (could be in separate file from mod_auth.c as long as registration occurs)
 */

#include "sys-crypto-md.h"
#include "base64.h"
#include "rand.h"
#include "http_header.h"

__attribute_cold__
static handler_t mod_auth_send_400_bad_request(request_st * const r) {

	/* a field was missing or invalid */
	r->http_status = 400; /* Bad Request */
	r->handler_module = NULL;

	return HANDLER_FINISHED;
}

static handler_t mod_auth_send_401_unauthorized_basic(request_st * const r, const buffer * const realm) {
	r->http_status = 401;
	r->handler_module = NULL;

	buffer * const tb = r->tmp_buf;
	buffer_copy_string_len(tb, CONST_STR_LEN("Basic realm=\""));
	buffer_append_string_buffer(tb, realm);
	buffer_append_string_len(tb, CONST_STR_LEN("\", charset=\"UTF-8\""));

	http_header_response_set(r, HTTP_HEADER_OTHER, CONST_STR_LEN("WWW-Authenticate"), CONST_BUF_LEN(tb));

	return HANDLER_FINISHED;
}

static handler_t mod_auth_check_basic(request_st * const r, void *p_d, const struct http_auth_require_t * const require, const struct http_auth_backend_t * const backend) {
	const buffer *b = http_header_request_get(r, HTTP_HEADER_AUTHORIZATION, CONST_STR_LEN("Authorization"));
	buffer *username;
	char *pw;
	handler_t rc = HANDLER_UNSET;

	UNUSED(p_d);

	if (NULL == backend) {
		log_error(r->conf.errh, __FILE__, __LINE__, "auth.backend not configured for %s", r->uri.path.ptr);
		r->http_status = 500;
		r->handler_module = NULL;
		return HANDLER_FINISHED;
	}

	if (NULL == b) {
		return mod_auth_send_401_unauthorized_basic(r, require->realm);
	}

	if (!buffer_eq_icase_ssn(b->ptr, CONST_STR_LEN("Basic "))) {
		return mod_auth_send_401_unauthorized_basic(r, require->realm);
	}
      #ifdef __COVERITY__
	if (buffer_string_length(b) < sizeof("Basic ")-1) {
		return mod_auth_send_400_bad_request(r);
	}
      #endif

	username = buffer_init();

	/* coverity[overflow_sink : FALSE] */
	if (!buffer_append_base64_decode(username, b->ptr+sizeof("Basic ")-1, buffer_string_length(b)-(sizeof("Basic ")-1), BASE64_STANDARD)) {
		log_error(r->conf.errh, __FILE__, __LINE__, "decoding base64-string failed %s", b->ptr+sizeof("Basic ")-1);

		buffer_free(username);
		return mod_auth_send_400_bad_request(r);
	}

	/* r2 == user:password */
	if (NULL == (pw = strchr(username->ptr, ':'))) {
		log_error(r->conf.errh, __FILE__, __LINE__, "missing ':' in %s", username->ptr);

		buffer_free(username);
		return mod_auth_send_400_bad_request(r);
	}

	buffer_string_set_length(username, pw - username->ptr);
	pw++;

	rc = backend->basic(r, backend->p_d, require, username, pw);
	switch (rc) {
	case HANDLER_GO_ON:
		http_auth_setenv(r, CONST_BUF_LEN(username), CONST_STR_LEN("Basic"));
		break;
	case HANDLER_WAIT_FOR_EVENT:
	case HANDLER_FINISHED:
		break;
	case HANDLER_ERROR:
	default:
		log_error(r->conf.errh, __FILE__, __LINE__,
		  "password doesn't match for %s username: %s IP: %s",
		  r->uri.path.ptr, username->ptr, r->con->dst_addr_buf->ptr);
		r->keep_alive = 0; /*(disable keep-alive if bad password)*/
		rc = HANDLER_UNSET;
		break;
	}

	buffer_free(username);
	return (HANDLER_UNSET != rc) ? rc : mod_auth_send_401_unauthorized_basic(r, require->realm);
}


#ifdef USE_LIB_CRYPTO

static void mod_auth_digest_mutate_sha256(http_auth_info_t *ai, const char *m, const char *uri, const char *nonce, const char *cnonce, const char *nc, const char *qop) {
    SHA256_CTX ctx;
    char a1[HTTP_AUTH_DIGEST_SHA256_BINLEN*2+1];
    char a2[HTTP_AUTH_DIGEST_SHA256_BINLEN*2+1];

    if (ai->dalgo & HTTP_AUTH_DIGEST_SESS) {
        SHA256_Init(&ctx);
        li_tohex(a1, sizeof(a1), (const char *)ai->digest, ai->dlen);
        SHA256_Update(&ctx, (unsigned char *)a1, sizeof(a1)-1);
        SHA256_Update(&ctx, CONST_STR_LEN(":"));
        SHA256_Update(&ctx, (unsigned char *)nonce, strlen(nonce));
        SHA256_Update(&ctx, CONST_STR_LEN(":"));
        SHA256_Update(&ctx, (unsigned char *)cnonce, strlen(cnonce));
        SHA256_Final(ai->digest, &ctx);
    }

    li_tohex(a1, sizeof(a1), (const char *)ai->digest, ai->dlen);

    /* calculate H(A2) */
    SHA256_Init(&ctx);
    SHA256_Update(&ctx, (unsigned char *)m, strlen(m));
    SHA256_Update(&ctx, CONST_STR_LEN(":"));
    SHA256_Update(&ctx, (unsigned char *)uri, strlen(uri));
  #if 0
    /* qop=auth-int not supported, already checked in caller */
    if (qop && buffer_eq_icase_ss(qop, strlen(qop), CONST_STR_LEN("auth-int"))){
        SHA256_Update(&ctx, CONST_STR_LEN(":"));
        SHA256_Update(&ctx, (unsigned char *) [body checksum], ai->dlen*2);
    }
  #endif
    SHA256_Final(ai->digest, &ctx);
    li_tohex(a2, sizeof(a2), (const char *)ai->digest, ai->dlen);

    /* calculate response */
    SHA256_Init(&ctx);
    SHA256_Update(&ctx, (unsigned char *)a1, sizeof(a1)-1);