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scep.c

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/**
 * @file scep.c
 * @brief SCEP specific functions
 * 
 * Contains functions to build SCEP request's and to parse SCEP reply's.
 */

/*
 * Copyright (C) 2005 Jan Hutter, Martin Willi
 * Hochschule fuer Technik Rapperswil
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * for more details.
 */

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

#include <freeswan.h>

#ifdef LIBCURL
#include <curl/curl.h>
#endif

#include "../pluto/constants.h"
#include "../pluto/defs.h"
#include "../pluto/rnd.h"
#include "../pluto/oid.h"
#include "../pluto/asn1.h"
#include "../pluto/pkcs1.h"
#include "../pluto/fetch.h"
#include "../pluto/log.h"

#include "scep.h"

static char ASN1_messageType_oid_str[] = {
    0x06, 0x0A, 0x60, 0x86, 0x48, 0x01, 0x86, 0xF8, 0x45, 0x01, 0x09, 0x02
};

static char ASN1_senderNonce_oid_str[] = {
    0x06, 0x0A, 0x60, 0x86, 0x48, 0x01, 0x86, 0xF8, 0x45, 0x01, 0x09, 0x05
};

static char ASN1_transId_oid_str[] = {
    0x06, 0x0A, 0x60, 0x86, 0x48, 0x01, 0x86, 0xF8, 0x45, 0x01, 0x09, 0x07
};

static const chunk_t ASN1_messageType_oid =
                  strchunk(ASN1_messageType_oid_str);
static const chunk_t ASN1_senderNonce_oid =
                  strchunk(ASN1_senderNonce_oid_str);
static const chunk_t ASN1_transId_oid =
                  strchunk(ASN1_transId_oid_str);

static const char *pkiStatus_values[] = { "0", "2", "3" };

static const char *pkiStatus_names[] = {
   "SUCCESS",
   "FAILURE",
   "PENDING",
   "UNKNOWN"
};

static const char *msgType_values[] = { "3", "19", "20", "21", "22" };

static const char *msgType_names[] = {
  "CertRep",
  "PKCSReq",
  "GetCertInitial",
  "GetCert",
  "GetCRL",
  "Unknown"
};

static const char *failInfo_reasons[] = {
  "badAlg - unrecognized or unsupported algorithm identifier",
  "badMessageCheck - integrity check failed",
  "badRequest - transaction not permitted or supported",
  "badTime - Message time field was not sufficiently close to the system time",
  "badCertId - No certificate could be identified matching the provided criteria"
};

const scep_attributes_t empty_scep_attributes = {
  SCEP_Unknown_MSG   , /* msgType */
  SCEP_UNKNOWN       , /* pkiStatus */
  SCEP_unknown_REASON, /* failInfo */
  { NULL, 0 }        , /* transID */
  { NULL, 0 }        , /* senderNonce */
  { NULL, 0 }        , /* recipientNonce */
};

/* ASN.1 definition of the X.501 atttribute type */

static const asn1Object_t attributesObjects[] = {
  { 0, "attributes",    ASN1_SET,   ASN1_LOOP }, /* 0 */
  { 1,   "attribute",   ASN1_SEQUENCE,    ASN1_NONE }, /* 1 */
  { 2,     "type",      ASN1_OID,   ASN1_BODY }, /* 2 */
  { 2,     "values",    ASN1_SET,   ASN1_LOOP }, /* 3 */
  { 3,       "value",   ASN1_EOC,   ASN1_RAW  }, /* 4 */
  { 2,     "end loop",  ASN1_EOC,   ASN1_END  }, /* 5 */
  { 0, "end loop",      ASN1_EOC,   ASN1_END  }, /* 6 */
};

#define ATTRIBUTE_OBJ_TYPE    2
#define ATTRIBUTE_OBJ_VALUE   4
#define ATTRIBUTE_OBJ_ROOF    7

/*
 * extract and store an attribute
 */
static bool
extract_attribute(int oid, chunk_t object, u_int level
, scep_attributes_t *attrs)
{
    asn1_t type = ASN1_EOC;
    const char *name = "none";

    switch (oid)
    {
    case OID_PKCS9_CONTENT_TYPE:
      type = ASN1_OID;
      name = "contentType";
      break;
    case OID_PKCS9_SIGNING_TIME:
      type = ASN1_UTCTIME;
      name = "signingTime";
      break;
    case OID_PKCS9_MESSAGE_DIGEST:
      type = ASN1_OCTET_STRING;
      name = "messageDigest";
      break;
    case OID_PKI_MESSAGE_TYPE:
      type = ASN1_PRINTABLESTRING;
      name = "messageType";
      break;
    case OID_PKI_STATUS:
      type = ASN1_PRINTABLESTRING;
      name = "pkiStatus";
      break;
    case OID_PKI_FAIL_INFO:
      type = ASN1_PRINTABLESTRING;
      name = "failInfo";
      break;
    case OID_PKI_SENDER_NONCE:
      type = ASN1_OCTET_STRING;
      name = "senderNonce";
       break;
    case OID_PKI_RECIPIENT_NONCE:
      type = ASN1_OCTET_STRING;
      name = "recipientNonce";
      break;
    case OID_PKI_TRANS_ID:
      type = ASN1_PRINTABLESTRING;
      name = "transID";
      break;
    default:
      break;
    }

    if (type == ASN1_EOC)
      return TRUE;

    if (!parse_asn1_simple_object(&object, type, level+1, name))
      return FALSE;

    switch (oid)
    {
    case OID_PKCS9_CONTENT_TYPE:
      break;
    case OID_PKCS9_SIGNING_TIME:
      break;
    case OID_PKCS9_MESSAGE_DIGEST:
      break;
    case OID_PKI_MESSAGE_TYPE:
      {
          scep_msg_t m;

          for (m = SCEP_CertRep_MSG; m < SCEP_Unknown_MSG; m++)
          {
            if (strncmp(msgType_values[m], object.ptr, object.len) == 0)
                attrs->msgType = m;
          }
          DBG(DBG_CONTROL,
            DBG_log("messageType:  %s", msgType_names[attrs->msgType])
          )
      }
      break;
    case OID_PKI_STATUS:
      {
          pkiStatus_t s;

          for (s = SCEP_SUCCESS; s < SCEP_UNKNOWN; s++)
          {
            if (strncmp(pkiStatus_values[s], object.ptr, object.len) == 0)
                attrs->pkiStatus = s;
          }
          DBG(DBG_CONTROL,
            DBG_log("pkiStatus:    %s", pkiStatus_names[attrs->pkiStatus])
          )
      }
      break;
    case OID_PKI_FAIL_INFO:
      if (object.len == 1
      && *object.ptr >= '0' && *object.ptr <= '4')
      {
          attrs->failInfo = (failInfo_t)(*object.ptr - '0');
      }
        if (attrs->failInfo != SCEP_unknown_REASON)
          plog("failInfo:     %s", failInfo_reasons[attrs->failInfo]);
      break;
    case OID_PKI_SENDER_NONCE:
      attrs->senderNonce = object;
      break;
    case OID_PKI_RECIPIENT_NONCE:
      attrs->recipientNonce = object;
      break;
    case OID_PKI_TRANS_ID:
      attrs->transID = object;
    }
    return TRUE;
}

/*
 * parse X.501 attributes
 */
bool
parse_attributes(chunk_t blob, scep_attributes_t *attrs)
{
    asn1_ctx_t ctx;
    chunk_t object;
    u_int level;
    int oid = OID_UNKNOWN;
    int objectID = 0;

    asn1_init(&ctx, blob, 0, FALSE, DBG_RAW);

    DBG(DBG_CONTROL | DBG_PARSING,
      DBG_log("parsing attributes")
    )
    while (objectID < ATTRIBUTE_OBJ_ROOF)
    {
      if (!extract_object(attributesObjects, &objectID
                     , &object, &level, &ctx))
           return FALSE;

      switch (objectID)
      {
      case ATTRIBUTE_OBJ_TYPE:
          oid = known_oid(object);
          break;
      case ATTRIBUTE_OBJ_VALUE:
         if (!extract_attribute(oid, object, level, attrs))
            return FALSE;
      }
      objectID++;
    }
    return TRUE;
}

/* generates a unique fingerprint of the pkcs10 request 
 * by computing an MD5 hash over it
 */
void
scep_generate_pkcs10_fingerprint(chunk_t pkcs10, chunk_t *fingerprint)
{
    char buf[MD5_DIGEST_SIZE];
    chunk_t digest = { buf, sizeof(buf) };

    /* the fingerprint is the MD5 hash in hexadecimal format */
    compute_digest(pkcs10, OID_MD5, &digest);
    fingerprint->len = 2*digest.len;
    fingerprint->ptr = alloc_bytes(fingerprint->len + 1, "fingerprint");
    datatot(digest.ptr, digest.len, 16, fingerprint->ptr, fingerprint->len + 1);
}

/* generate a transaction id as the MD5 hash of an public key
 * the transaction id is also used as a unique serial number
 */
void
scep_generate_transaction_id(const RSA_public_key_t *rsak
, chunk_t *transID, chunk_t *serialNumber)
{
    char buf[MD5_DIGEST_SIZE];

    chunk_t digest = { buf, sizeof(buf) };
    chunk_t public_key = pkcs1_build_publicKeyInfo(rsak);

    bool msb_set;
    u_char *pos;

    compute_digest(public_key, OID_MD5, &digest);
    pfree(public_key.ptr);

    /* is the most significant bit of the digest set? */
    msb_set = (*digest.ptr & 0x80) == 0x80;

    /* allocate space for the serialNumber */
    serialNumber->len = msb_set + digest.len;
    serialNumber->ptr = alloc_bytes(serialNumber->len, "serialNumber");

    /* the serial number as the two's complement of the digest */
    pos = serialNumber->ptr;
    if (msb_set)
    {
      *pos++ = 0x00;
    }
    memcpy(pos, digest.ptr, digest.len);

    /* the transaction id is the serial number in hex format */
    transID->len = 2*digest.len;
    transID->ptr = alloc_bytes(transID->len + 1, "transID");
    datatot(digest.ptr, digest.len, 16, transID->ptr, transID->len + 1);
}

/*
 * builds a transId attribute
 */
chunk_t
scep_transId_attribute(chunk_t transID)
{
    return asn1_wrap(ASN1_SEQUENCE, "cm"
            , ASN1_transId_oid
            , asn1_wrap(ASN1_SET, "m"
                , asn1_simple_object(ASN1_PRINTABLESTRING, transID)
              )
            );
}

/*
 * builds a messageType attribute
 */
chunk_t
scep_messageType_attribute(scep_msg_t m)
{
    chunk_t msgType = {
      msgType_values[m],
      strlen(msgType_values[m])
    };

    return asn1_wrap(ASN1_SEQUENCE, "cm"
            , ASN1_messageType_oid
            , asn1_wrap(ASN1_SET, "m"
                , asn1_simple_object(ASN1_PRINTABLESTRING, msgType)
              )
            );
}

/*
 * builds a senderNonce attribute
 */
chunk_t
scep_senderNonce_attribute(void)
{
    const size_t nonce_len = 16;
    u_char nonce_buf[nonce_len];
    chunk_t senderNonce = { nonce_buf, nonce_len };

    get_rnd_bytes(nonce_buf, nonce_len);
 
    return asn1_wrap(ASN1_SEQUENCE, "cm"
            , ASN1_senderNonce_oid
            , asn1_wrap(ASN1_SET, "m"
                , asn1_simple_object(ASN1_OCTET_STRING, senderNonce)
              )
            );
}

/*
 * builds a pkcs7 enveloped and signed scep request
 */
chunk_t
scep_build_request(chunk_t data, chunk_t transID, scep_msg_t msg
, const x509cert_t *enc_cert, int enc_alg
, const x509cert_t *signer_cert, int digest_alg
, const RSA_private_key_t *private_key)
{
    chunk_t envelopedData, attributes, request;

    envelopedData = pkcs7_build_envelopedData(data, enc_cert, enc_alg);

    attributes = asn1_wrap(ASN1_SET, "mmmmm"
                , pkcs7_contentType_attribute()
                , pkcs7_messageDigest_attribute(envelopedData
                  , digest_alg)
                , scep_transId_attribute(transID)
                , scep_messageType_attribute(msg)
                , scep_senderNonce_attribute());

    request = pkcs7_build_signedData(envelopedData, attributes
                , signer_cert, digest_alg, private_key);
    freeanychunk(envelopedData);
    freeanychunk(attributes);
    return request;
}

#ifdef LIBCURL
/* converts a binary request to base64 with 64 characters per line
 * newline and '+' characters are escaped by %0A and %2B, respectively
 */
static char*
escape_http_request(chunk_t req)
{
    char *escaped_req = NULL;
    char *p1, *p2;
    int lines = 0;
    int plus  = 0;
    int n     = 0;

    /* compute and allocate the size of the base64-encoded request */
    int len = 1 + 4*((req.len + 2)/3);
    char *encoded_req = alloc_bytes(len, "encoded request");

    /* do the base64 conversion */
    len = datatot(req.ptr, req.len, 64, encoded_req, len);

    /* compute newline characters to be inserted every 64 characters */
    lines = (len - 2) / 64;

    /* count number of + characters to be escaped */
    p1 = encoded_req;
    while (*p1 != '\0')
    {
      if (*p1++ == '+')
          plus++;
    }

    escaped_req = alloc_bytes(len + 3*(lines + plus), "escaped request");

    /* escape special characters in the request */
    p1 = encoded_req;
    p2 = escaped_req;
    while (*p1 != '\0')
    {
      if (n == 64)
      {
          memcpy(p2, "%0A", 3);
          p2 += 3;
          n = 0;
      }
      if (*p1 == '+')
      {
          memcpy(p2, "%2B", 3);
          p2 += 3;
      }
      else
      {
          *p2++ = *p1;
      }
      p1++;
      n++;
    }
    *p2 = '\0';
    pfreeany(encoded_req);
    return escaped_req;
}
#endif

/*
 * send a SCEP request via HTTP and wait for a response
 */
bool
scep_http_request(const char *url, chunk_t pkcs7, scep_op_t op
, fetch_request_t req_type, chunk_t *response)
{
#ifdef LIBCURL
    char errorbuffer[CURL_ERROR_SIZE] = "";
    char *complete_url = NULL;
    struct curl_slist *headers = NULL;
    CURL *curl;
    CURLcode res;

    /* initialize response */
    *response = empty_chunk;

    /* initialize curl context */
    curl = curl_easy_init();
    if (curl == NULL)
    {
      plog("could not initialize curl context");
      return FALSE;
    }

    if (op == SCEP_PKI_OPERATION)
    {
      const char operation[] = "PKIOperation";

      if (req_type == FETCH_GET)
      {
          char *escaped_req = escape_http_request(pkcs7);

          /* form complete url */
          int len = strlen(url) + 20 + strlen(operation) + strlen(escaped_req) + 1;

          complete_url = alloc_bytes(len, "complete url");
          snprintf(complete_url, len, "%s?operation=%s&message=%s"
                , url, operation, escaped_req);
          pfreeany(escaped_req);

          curl_easy_setopt(curl, CURLOPT_HTTPGET, TRUE);
          headers = curl_slist_append(headers, "Pragma:");
          headers = curl_slist_append(headers, "Host:");
          headers = curl_slist_append(headers, "Accept:");
          curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers); 
          curl_easy_setopt(curl, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_0);
      }
      else /* HTTP_POST */
      {
          /* form complete url */
          int len = strlen(url) + 11 + strlen(operation) + 1;

          complete_url = alloc_bytes(len, "complete url");
          snprintf(complete_url, len, "%s?operation=%s", url, operation);

          curl_easy_setopt(curl, CURLOPT_HTTPGET, FALSE);
          headers = curl_slist_append(headers, "Content-Type:");
          headers = curl_slist_append(headers, "Expect:");
          curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers); 
          curl_easy_setopt(curl, CURLOPT_POSTFIELDS, pkcs7.ptr);
          curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, pkcs7.len);
      }
    }
    else  /* SCEP_GET_CA_CERT */
    {
      const char operation[] = "GetCACert";

      /* form complete url */
      int len = strlen(url) + 32 + strlen(operation) + 1;

      complete_url = alloc_bytes(len, "complete url");
      snprintf(complete_url, len, "%s?operation=%s&message=CAIdentifier"
            , url, operation);

      curl_easy_setopt(curl, CURLOPT_HTTPGET, TRUE);
    }

    curl_easy_setopt(curl, CURLOPT_URL, complete_url);
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_buffer);
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)response);
    curl_easy_setopt(curl, CURLOPT_ERRORBUFFER, errorbuffer);
    curl_easy_setopt(curl, CURLOPT_FAILONERROR, TRUE);
    curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, FETCH_CMD_TIMEOUT);
      
    DBG(DBG_CONTROL,
      DBG_log("sending scep request to '%s'", url)
    )
    res = curl_easy_perform(curl);
      
    if (res == CURLE_OK)
    {
      DBG(DBG_CONTROL,
          DBG_log("received scep response")
      )
      DBG(DBG_RAW,
          DBG_dump_chunk("SCEP response:\n", *response)
      )
    }
    else
    {
      plog("failed to fetch scep response from '%s': %s", url, errorbuffer);
    }
    curl_slist_free_all(headers);
    curl_easy_cleanup(curl);
    pfreeany(complete_url);

    return (res == CURLE_OK);
#else   /* !LIBCURL */
    plog("scep error: pluto wasn't compiled with libcurl support");
    return FALSE;
#endif  /* !LIBCURL */
}

err_t
scep_parse_response(chunk_t response, chunk_t transID, contentInfo_t *data
, scep_attributes_t *attrs, x509cert_t *signer_cert)
{
    chunk_t attributes;

    if (!pkcs7_parse_signedData(response, data, NULL, &attributes, signer_cert))
    {
      return "error parsing the scep response";
    }
    if (!parse_attributes(attributes, attrs))
    {
      return "error parsing the scep response attributes";
    }
    if (!same_chunk(transID, attrs->transID))
    {
      return "transaction ID of scep response does not match";
    }
    return NULL;
}

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