dkimverify.cpp

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/*****************************************************************************
*
*  Licensed under the Apache License, Version 2.0 (the "License"); 
*  you may not use this file except in compliance with the License. 
*  You may obtain a copy of the License at 
*
*      http://www.apache.org/licenses/LICENSE-2.0 
*
*  This code incorporates intellectual property owned by Yahoo! and licensed 
*  pursuant to the Yahoo! DomainKeys Patent License Agreement.
*
*  Unless required by applicable law or agreed to in writing, software 
*  distributed under the License is distributed on an "AS IS" BASIS, 
*  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
*  See the License for the specific language governing permissions and 
*  limitations under the License.
*
*  Changes done by ¢feh@fehcom.de obeying the above license
*
*****************************************************************************/
#include <string.h>
#include <ctype.h>
#include <assert.h>
#include <vector>
#include <algorithm>
#include "dkim.h"
#include "dkimverify.h"
#include "dnsgettxt.h"
extern "C" { 
#include "dns.h"
#include "stralloc.h"
}
 
/*****************************************************************************
*
* Verifying DKIM Ed25519 signatures:
*
* The received DKIM header includes two cryptographic relevant informations:
*
* a) The 'body hash' => bh=[sha1|sha256]
* b) The signature   =>  b=[RSA-SHA1|RSA-SHA256|PureEd25519]
*
* Several DKIM headers (=signatures) may be present in the email. 
* Here, it is limited to max. Shall we really evaluate all?
*
* Caution: Using hybrid signatures, calling the destructor will core dump 
*          given EVP_MD_CTX_free() upon the next call of EVP_DigestInit.
*          Using the destructor with EVP_MD_CTX_reset() however works.
*
*****************************************************************************/
 
#define _strnicmp strncasecmp
#define _stricmp strcasecmp
#define MAX_SIGNATURES  10  // maximum number of DKIM signatures to process/message
#define FDLOG stderr  /* writing to another FD requires a method */
 
string SigHdr;
size_t m_SigHdr;
 
extern "C" int stralloc_copys(stralloc *,char const *);
 
int dig_ascii(char *digascii,unsigned const char *digest,const int len)
{
  static const char hextab[] = "0123456789abcdef";
  int j;
 
  for (j = 0; j < len; j++) {
    digascii[2 * j] = hextab[(unsigned char)digest[j] >> 4];
    digascii[2 * j + 1] = hextab[(unsigned char)digest[j] & 0x0f];
  }
  digascii[2 * len] = '\0';
 
  return (2 * j);  // 2*len
}
 
 
int _DNSGetTXT(const char *szFQDN,char *Buffer,int nBufLen)
{
   stralloc out = {0};
   stralloc sa = {0};
   Buffer[0] = '\0';  // need to be initialized
 
   if (!szFQDN) return -1;
   if (!stralloc_copys(&sa,szFQDN)) return -1;
   
   DNS_INIT
   
   switch (dns_txt(&out,&sa)) {
     case -1: return -1;
     case  0: return 0;
   } 
 
   if (nBufLen < out.len) 
     return -2;
 
   if (!stralloc_0(&out)) return -1;
   memcpy(Buffer,out.s,out.len);  // Return-by-value; sigh
 
   return out.len;
}
 
int _DKIM_ReportResult(const char* ResFile,const char* result,const char* reason)
{
  int len = 0;
 
  FILE* out = fopen(ResFile,"wb+");
  if (out == NULL) return -1;
 
  if (result) {
    len = strlen(result);
    fwrite(result,1,len,out);
    fwrite("\r",1,1,out);
  }
 
  if (reason) {
    fwrite(reason,1,strlen(reason),out);
    fwrite("\r",1,1,out);
  }
  fclose(out);
 
  return len;
}
 
const char* DKIM_ErrorResult(const int res)
{
  const char* errormsg = "";
 
  switch (res) {
    case DKIM_FAIL:
      errormsg = " (verify error: message is suspicious)";
      break;
    case DKIM_BAD_SYNTAX:
      errormsg = " (signature error: could not parse or has bad tags/values)";
      break;
    case DKIM_SIGNATURE_BAD:
      errormsg = " (signature error: RSA/ED25519 verify failed)";
      break;
    case DKIM_SIGNATURE_BAD_BUT_TESTING:
      errormsg = " (signature error: RSA/ED25519 verify failed but testing)";
      break;
    case DKIM_SIGNATURE_EXPIRED:
      errormsg = " (signature error: signature x= value expired)";
      break;
    case DKIM_SELECTOR_INVALID:
      errormsg = " (signature error: selector doesn't parse or contains invalid values)";
      break;
    case DKIM_SELECTOR_GRANULARITY_MISMATCH:
      errormsg = " (signature error: selector g= doesn't match i=)";
      break;
    case DKIM_SELECTOR_KEY_REVOKED:
      errormsg = " (signature error: revoked p= empty)";
      break;
    case DKIM_SELECTOR_DOMAIN_NAME_TOO_LONG:
      errormsg = " (dns error: selector domain name too long to request)";
      break;
    case DKIM_SELECTOR_DNS_TEMP_FAILURE:
      errormsg = " (dns error: temporary dns failure requesting selector)";
      break;
    case DKIM_SELECTOR_DNS_PERM_FAILURE:
      errormsg = " (dns error: permanent dns failure requesting selector)";
      break;
    case DKIM_SELECTOR_PUBLIC_KEY_INVALID:
      errormsg = " (signature error: selector p= value invalid or wrong format)";
      break;
    case DKIM_NO_SIGNATURES:
      errormsg = " (process error: no signatures)";
      break;
    case DKIM_NO_VALID_SIGNATURES:
      errormsg = " (process error: no valid signatures)";
      break;
    case DKIM_BODY_HASH_MISMATCH:
      errormsg = " (signature verify error: message body does not hash to bh= value)";
      break;
    case DKIM_SELECTOR_ALGORITHM_MISMATCH:
      errormsg = " (signature error: selector h= doesn't match signature a=)";
      break;
    case DKIM_STAT_INCOMPAT:
      errormsg = " (signature error: incompatible v= value)";
      break;
    case DKIM_UNSIGNED_FROM:
      errormsg = " (signature error: not all message's From headers in signature)";
      break;
    case DKIM_OUT_OF_MEMORY:
      errormsg = " (internal error: memory allocation failed)";
      break;
    case DKIM_INVALID_CONTEXT:
      errormsg = " (internal error: DKIMContext structure invalid for this operation)";
      break;
    case DKIM_NO_SENDER:
      errormsg = " (signing error: Could not find From: or Sender: header in message)";
      break;
    case DKIM_BAD_PRIVATE_KEY:
      errormsg = " (signing error: Could not parse private key)";
      break;
    case DKIM_BUFFER_TOO_SMALL:
      errormsg = " (signing error: Buffer passed in is not large enough)";
      break;
  }
 
  return errormsg;
}
 
SignatureInfo::SignatureInfo(bool s)
{
  VerifiedBodyCount = 0;
  UnverifiedBodyCount = 0;
 
  m_Hdr_ctx = EVP_MD_CTX_new();
  m_Bdy_ctx = EVP_MD_CTX_new();
  m_Msg_ctx = EVP_MD_CTX_new();
  m_pSelector = NULL;
  Status = DKIM_SUCCESS;
  m_nHash = 0;
  EmptyLineCount = 0;
  m_SaveCanonicalizedData = s;
}
 
SignatureInfo::~SignatureInfo()
{
  EVP_MD_CTX_reset(m_Hdr_ctx);  
  EVP_MD_CTX_reset(m_Bdy_ctx);
  EVP_MD_CTX_reset(m_Msg_ctx);
}
 
inline bool isswsp(char ch)
{
  return (ch == ' ' || ch == '\t' || ch == '\r' || ch == '\n');
}
 
// 
// Parse a DKIM tag-list.  Returns true for success
//
bool ParseTagValueList(char *tagvaluelist,const char *wanted[],char *values[])
{
  char *s = tagvaluelist;
 
  for (;;) {
    // skip whitespace
    while (isswsp(*s))
      s++;
 
    // if at the end of the string, return success.  Note: this allows a list with no entries
    if (*s == '\0')
      return true;
 
    // get tag name
    if (!isalpha(*s))
      return false;
 
    char *tag = s;
    do {
      s++;
    } while (isalnum(*s) || *s == '-');
 
    char *endtag = s;
 
    // skip whitespace before equals
    while (isswsp(*s))
      s++;
 
    // next character must be equals
    if (*s != '=')
      return false;
    s++;
 
    // null-terminate tag name
    *endtag = '\0';
 
    // skip whitespace after equals
    while (isswsp(*s))
      s++;
 
    // get tag value
    char *value = s;
 
    while (*s != ';' && ((*s == '\t' || *s == '\r' || *s == '\n') || (*s >= ' ' && *s <= '~')))
      s++;
 
    char *e = s;
 
    // make sure the next character is the null terminator (which means we're done) or a semicolon (not done)
    bool done = false;
    if (*s == '\0')
      done = true;
    else {
      if (*s != ';')
        return false;
      s++;
    }
 
    // skip backwards past any trailing whitespace
    while (e > value && isswsp(e[-1]))
      e--;
 
    // null-terminate tag value
    *e = '\0';
 
    // check to see if we want this tag
    for (unsigned i = 0; wanted[i] != NULL; i++) {
      if (strcmp(wanted[i],tag) == 0) {
        // return failure if we already have a value for this tag (duplicates not allowed)
        if (values[i] != NULL)
          return false;
        values[i] = value;
        break;
      }
    }
 
    if (done)
      return true;
  }
}
//
// Convert hex char to value (0-15)
//
char Tohex(char ch)
{
  if (ch >= '0' && ch <= '9')
    return (ch - '0');
  else if (ch >= 'A' && ch <= 'F')
    return (ch - 'A' + 10);
  else if (ch >= 'a' && ch <= 'f')
    return (ch - 'a' + 10);
  else {
    assert(0);
    return 0;
  }
}
// 
// Decode quoted printable string in-place
//
void DecodeQuotedPrintable(char* ptr)
{
  char *s = ptr;
  while (*s != '\0' && *s != '=')
    s++;
 
  if (*s == '\0')
    return;
 
  char *d = s;
  do {
    if (*s == '=' && isxdigit(s[1]) && isxdigit(s[2])) {
      *d++ = (Tohex(s[1]) << 4) | Tohex(s[2]);
      s += 3;
    } else {
      *d++ = *s++;
    }
  } while (*s != '\0');
  *d = '\0';
}
// 
// Decode base64 string in-place, returns number of bytes output
//
unsigned DecodeBase64(char *ptr)
{
  static const unsigned char base64_table[256] = {
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255, 62,255,255,255, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61,255,255,255,255,255,255,
    255,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,255,255,255,255,255,
    255, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255 };
 
  unsigned char* s = (unsigned char* )ptr;
  unsigned char* d = (unsigned char* )ptr;
  unsigned b64accum = 0;
  unsigned char b64shift = 0;
 
  while (*s != '\0') {
    unsigned char value = base64_table[*s++];
    if ((signed char) value >= 0) {
      b64accum = (b64accum << 6) | value;
      b64shift += 6;
      if (b64shift >= 8) {
        b64shift -= 8;
        *d++ = (b64accum >> b64shift);
      }
    }
  }
 
  return (char* )d-ptr;
}
 
// 
// Match a string with a pattern (used for g= value)
// Supports a single, optional "*" wildcard character.
//
bool WildcardMatch(const char *p, const char *s)
{
  // special case: An empty "g=" value never matches any addresses
  if (*p == '\0')
    return false;
 
  const char* wildcard = strchr(p,'*');
  if (wildcard == NULL) {
    return strcmp(s, p) == 0;
  } else {
    unsigned beforewildcardlen = wildcard - p;
    unsigned afterwildcardlen = strlen(wildcard + 1);
    unsigned slen = strlen(s);
    return (slen >= beforewildcardlen + afterwildcardlen) && 
      (strncmp(s,p,beforewildcardlen) == 0) && strcmp(s + slen - afterwildcardlen,wildcard + 1) == 0;
  }
}
 
// 
// Parse addresses from a string.  Returns true if at least one address found
//
bool ParseAddresses(string str,vector<string> &Addresses)
{
  char* s = (char* )str.c_str();
 
  while (*s != '\0') {
    char* start = s;
    char* from = s;
    char* to = s;
    char* lt = NULL;  // pointer to less than character (<) which starts the address if found
 
    while (*from != '\0') {
      if (*from == '(') {
        // skip over comment
        from++;
        for (int depth = 1; depth != 0; from++) {
          if (*from == '\0')
            break;
          else if (*from == '(')
            depth++;
          else if (*from == ')')
            depth--;
          else if (*from == '\\' && from[1] != '\0')
            from++;
        }
      }
      else if (*from == ')') {
        // ignore closing parenthesis outside of comment
        from++;
      } else if (*from == ',' || *from == ';') {
        // comma/semicolon ends the address
        from++;
        break;
      }
      else if (*from == ' ' || *from == '\t' || *from == '\r' || *from == '\n') {
        // ignore whitespace
        from++;
      } else if (*from == '"') {
        // copy the contents of a quoted string
        from++;
        while (*from != '\0') {
          if (*from == '"') {
            from++;
            break;
          } else if (*from == '\\' && from[1] != '\0')
            *to++ = *from++;
          *to++ = *from++;
        }
      } else if (*from == '\\' && from[1] != '\0') {
        // copy quoted-pair
        *to++ = *from++;
        *to++ = *from++;
      } else {
        // copy any other char
        *to = *from++;
        // save pointer to '<' for later...
        if (*to == '<')
          lt = to;
        to++;
      }
    }
 
    *to = '\0';
 
    // if there's < > get what's inside
    if (lt != NULL) {
      start = lt+1;
      char *gt = strchr(start, '>');
      if (gt != NULL)
        *gt = '\0';
    } else {
      // look for and strip group name
      char *colon = strchr(start, ':');
      if (colon != NULL) {
        char *at = strchr(start, '@');
        if (at == NULL || colon < at)
          start = colon+1;
      }
    }
 
    if (*start != '\0' && strchr(start, '@') != NULL) {
      Addresses.push_back(start);   // save address
    }
 
    s = from;
  }
 
  return !Addresses.empty();
}
 
 
CDKIMVerify::CDKIMVerify()
{
  m_pfnSelectorCallback = NULL;
//  m_pfnPracticesCallback = NULL;
  m_HonorBodyLengthTag = false;
  m_CheckPractices = false;
// Kai:
//  m_SubjectIsRequired = true;
  m_SubjectIsRequired = false;
  m_SaveCanonicalizedData = false;
  m_AllowUnsignedFromHeaders = false;
}
 
CDKIMVerify::~CDKIMVerify() {} // Destructor
 
// 
// Init - save the options
//
int CDKIMVerify::Init(DKIMVerifyOptions* pOptions)
{
  int nRet = CDKIMBase::Init();
 
  m_pfnSelectorCallback = pOptions->pfnSelectorCallback;
  // m_pfnPracticesCallback = pOptions->pfnPracticesCallback;
 
  m_HonorBodyLengthTag = pOptions->nHonorBodyLengthTag != 0;
  m_CheckPractices = pOptions->nCheckPractices != 0;
// Kai:
//  m_SubjectIsRequired = pOptions->nSubjectRequired == 0;
  m_SubjectIsRequired = pOptions->nSubjectRequired == 1;
  m_SaveCanonicalizedData = pOptions->nSaveCanonicalizedData != 0;
  m_AllowUnsignedFromHeaders = pOptions->nAllowUnsignedFromHeaders != 0;
 
  return nRet;
}
 
// 
// GetResults - return the pass/fail/neutral verification result
//
int CDKIMVerify::GetResults(void)
{
  // char mdi[128];
  // char digi[128];
   
  ProcessFinal();
 
  unsigned char *SignMsg;
  unsigned SuccessCount = 0;
  int TestingFailures = 0;
  int RealFailures = 0;
  int res = 0;
 
  list<string> SuccessfulDomains;  // can contain duplicates
 
  for (list<SignatureInfo>::iterator i = Signatures.begin(); i != Signatures.end(); ++i) {
    if (i->Status == DKIM_SUCCESS) {
      if (!i->BodyHashData.empty()) {  // FIRST: Get the body hash
        unsigned char md[EVP_MAX_MD_SIZE];
        unsigned len = 0;
 
        res = EVP_DigestFinal_ex(i->m_Bdy_ctx,md,&len);  
        EVP_MD_CTX_reset(i->m_Bdy_ctx);
        // dig_ascii(digi,md,32);
        // dig_ascii(mdi,(unsigned const char *)i->BodyHashData.data(),32);
 
        if (!res || len != i->BodyHashData.length() || memcmp(i->BodyHashData.data(),md,len) != 0) {
          // body hash mismatch
 
          // if the selector is in testing mode...
          if (i->m_pSelector->Testing) {
            i->Status = DKIM_SIGNATURE_BAD_BUT_TESTING;  // todo: make a new error code for this?
            TestingFailures++;
          } else {
            i->Status = DKIM_BODY_HASH_MISMATCH;
            RealFailures++;
          }
          continue;  // next signature
        }
      } else {
        // hash CRLF separating the body from the signature
        i->Hash("\r\n",2);
      }
 
      // SECOND: Fetch the signature
 
      string sSignedSig = i->Header;
      string sSigValue = sSignedSig.substr(sSignedSig.find(':') + 1);
 
      static const char* tags[] = {"b",NULL};
      char* values[sizeof(tags)/sizeof(tags[0])] = {NULL};
 
      char* pSigValue = (char* ) sSigValue.c_str();   // our signature
      if (ParseTagValueList(pSigValue,tags,values) && values[0] != NULL) {
        sSignedSig.erase(15 + values[0] - pSigValue,strlen(values[0]));
      }
 
      if (i->HeaderCanonicalization == DKIM_CANON_RELAXED) {
        sSignedSig = RelaxHeader(sSignedSig);
      }
      else if (i->HeaderCanonicalization == DKIM_CANON_NOWSP) {
        RemoveSWSP(sSignedSig);
        // convert "DKIM-Signature" to lower case
        sSignedSig.replace(0,14,"dkim-signature",14);
      }
 
      i->Hash(sSignedSig.c_str(),sSignedSig.length());   // include generated DKIM signature header 
      assert(i->m_pSelector != NULL);
 
      if (EVP_PKEY_base_id(i->m_pSelector->PublicKey) != EVP_PKEY_ED25519) 
        res = EVP_VerifyFinal(i->m_Hdr_ctx,(unsigned char *)i->SignatureData.data(),i->SignatureData.length(),i->m_pSelector->PublicKey);
      else if (EVP_PKEY_base_id(i->m_pSelector->PublicKey) == EVP_PKEY_ED25519) {
        EVP_DigestVerifyInit(i->m_Msg_ctx,NULL,NULL,NULL,i->m_pSelector->PublicKey);  // late initialization
 
        SignMsg = (unsigned char *) SigHdr.data();
        res = EVP_DigestVerify(i->m_Msg_ctx,(unsigned char *)i->SignatureData.data(),(size_t)i->SignatureData.length(),
                               SignMsg,m_SigHdr);
      }
 
      if (res == 1) {
        if (i->UnverifiedBodyCount == 0)
          i->Status = DKIM_SUCCESS;
        else
          i->Status = DKIM_SUCCESS_BUT_EXTRA;
        SuccessCount++;
        SuccessfulDomains.push_back(i->Domain);
      } else {
        // if the selector is in testing mode...
        if (i->m_pSelector->Testing) {
          i->Status = DKIM_SIGNATURE_BAD_BUT_TESTING;
          TestingFailures++;
        } else {
          i->Status = DKIM_SIGNATURE_BAD;
          RealFailures++;
        }
      }
    } else if (i->Status == DKIM_SELECTOR_GRANULARITY_MISMATCH || 
               i->Status == DKIM_SELECTOR_ALGORITHM_MISMATCH || 
               i->Status == DKIM_SELECTOR_KEY_REVOKED) {
      // treat these as failures
      // todo: maybe see if the selector is in testing mode?
      RealFailures++;
    }
  }    // loop over signature infos done
 
 
  // get the From address's domain if we might need it
  string sFromDomain;
  if (SuccessCount > 0 || m_CheckPractices) {
    for (list<string>::iterator i = HeaderList.begin(); i != HeaderList.end(); ++i) {
      if (_strnicmp(i->c_str(),"From",4) == 0) {
        // skip over whitespace between the header name and :
        const char* s = i->c_str() + 4;
        while (*s == ' ' || *s == '\t')
          s++;
        if (*s == ':') {
          vector<string> Addresses;
          if (ParseAddresses(s + 1, Addresses)) {
            unsigned atpos = Addresses[0].find('@');
            sFromDomain = Addresses[0].substr(atpos + 1);
            break;
          }
        }
      }
    }
  }
 
  // if a signature from the From domain verified successfully, return success now
  // without checking the author domain signing practices
  if (SuccessCount > 0 && !sFromDomain.empty()) {
    for (list<string>::iterator i = SuccessfulDomains.begin(); i != SuccessfulDomains.end(); ++i) {
      // see if the successful domain is the same as or a parent of the From domain
      if (i->length() > sFromDomain.length())
        continue;
      if (_stricmp(i->c_str(),sFromDomain.c_str() + sFromDomain.length() - i->length()) != 0)
        continue;
      if (i->length() == sFromDomain.length() || sFromDomain.c_str()[sFromDomain.length() - i->length() - 1] == '.') {
        return SuccessCount == Signatures.size() ? DKIM_SUCCESS : DKIM_PARTIAL_SUCCESS;
      }
    }
  }
 
  /* Removed obsolete ADSP check */
 
  // return neutral for everything else
  return DKIM_NEUTRAL;
}
 
// 
// Hash - update the hash or update the Ed25519 signature input
//
void SignatureInfo::Hash(const char* szBuffer,unsigned nBufLength,bool IsBody)
{
#if 0
  if(nBufLength == 2 && szBuffer[0] == '\r' && szBuffer[1] == '\n')
  {
    printf("[CRLF]\n");
  } else {
    char* szDbg = new char[nBufLength+1];
    strncpy(szDbg, szBuffer, nBufLength);
    szDbg[nBufLength] = '\0';
    printf("[%s]\n", szDbg);
  }
#endif
 
  if (IsBody && BodyLength != (unsigned) -1) {    // trick: 2's complement 
    VerifiedBodyCount += nBufLength;
    if (VerifiedBodyCount > BodyLength) {
      nBufLength = BodyLength - (VerifiedBodyCount - nBufLength);
      UnverifiedBodyCount += VerifiedBodyCount - BodyLength;
      VerifiedBodyCount = BodyLength;
      if (nBufLength == 0) return;
    }
  }
 
  if (IsBody && !BodyHashData.empty()) {
    EVP_DigestUpdate(m_Bdy_ctx,szBuffer,nBufLength);
  } else {
    EVP_VerifyUpdate(m_Hdr_ctx,szBuffer,nBufLength);
    SigHdr.append(szBuffer,nBufLength);
    m_SigHdr += nBufLength;
  }
 
  if (m_SaveCanonicalizedData) {
    CanonicalizedData.append(szBuffer,nBufLength);
  }
}
 
 
// 
// ProcessHeaders - Look for DKIM-Signatures and start processing them
//                  look for DKIM-Signature header(s)
//
int CDKIMVerify::ProcessHeaders(void)
{
  for (list<string>::iterator i = HeaderList.begin(); i != HeaderList.end(); ++i) {
    if (strlen(i->c_str()) < 14) continue; // too short
    if (_strnicmp(i->c_str(),"DKIM-Signature",14) == 0) {
      // skip over whitespace between the header name and :
      const char *s = i->c_str() + 14;
      while (*s == ' ' || *s == '\t')
        s++;
      if (*s == ':') {
        // found
        SignatureInfo sig(m_SaveCanonicalizedData);
        sig.Status = ParseDKIMSignature(*i,sig);
        Signatures.push_back(sig);    // save signature
 
        if (Signatures.size() >= MAX_SIGNATURES)
          break;
      }
    }
  }
 
  if (Signatures.empty())
    return DKIM_NO_SIGNATURES;
 
  bool ValidSigFound = false;
 
  for (list<SignatureInfo>::iterator s = Signatures.begin(); s != Signatures.end(); ++s) {
    SignatureInfo &sig = *s;
    if (sig.Status != DKIM_SUCCESS) continue;
    SelectorInfo &sel = GetSelector(sig.Selector,sig.Domain);
    sig.m_pSelector = &sel;
 
    if (sel.Status != DKIM_SUCCESS) {
      sig.Status = sel.Status;
    } else {
      // check the granularity
      if (!WildcardMatch(sel.Granularity.c_str(),sig.IdentityLocalPart.c_str()))
        sig.Status = DKIM_SELECTOR_GRANULARITY_MISMATCH;    // this error causes the signature to fail
 
      // check the hash algorithm
      if ((sig.m_nHash == DKIM_HASH_SHA1 && !sel.AllowSHA1) || 
          (sig.m_nHash == DKIM_HASH_SHA256 && !sel.AllowSHA256))
        sig.Status = DKIM_SELECTOR_ALGORITHM_MISMATCH;      // causes signature to fail
 
      // check for same domain
      if (sel.SameDomain && _stricmp(sig.Domain.c_str(),sig.IdentityDomain.c_str()) != 0)
        sig.Status = DKIM_BAD_SYNTAX;
    }
 
    if (sig.Status != DKIM_SUCCESS) continue;
 
    // initialize the hashes
    if (sig.m_nHash == DKIM_HASH_SHA1) {
      EVP_VerifyInit_ex(sig.m_Hdr_ctx,EVP_sha1(),NULL);
      EVP_DigestInit_ex(sig.m_Bdy_ctx,EVP_sha1(),NULL);
    }
    if (sig.m_nHash == DKIM_HASH_SHA256) {
      EVP_VerifyInit_ex(sig.m_Hdr_ctx,EVP_sha256(),NULL);
      EVP_DigestInit_ex(sig.m_Bdy_ctx,EVP_sha256(),NULL);
      SigHdr.assign("");
      m_SigHdr = 0;
    }
 
    // compute the hash of the header
    vector<list<string>::reverse_iterator> used;
 
    for (vector<string>::iterator x = sig.SignedHeaders.begin(); x != sig.SignedHeaders.end(); ++x) {
      list<string>::reverse_iterator i;
      for (i = HeaderList.rbegin(); i != HeaderList.rend(); ++i) {
        if (_strnicmp(i->c_str(),x->c_str(),x->length()) == 0) {
          // skip over whitespace between the header name and :
          const char* s = i->c_str()+x->length();
          while (*s == ' ' || *s == '\t')
            s++;
          if (*s == ':' && find(used.begin(),used.end(),i) == used.end())
            break;
        }
      }
 
      if (i != HeaderList.rend()) {
        used.push_back(i);
 
        // hash this header
        if (sig.HeaderCanonicalization == DKIM_CANON_SIMPLE) {
          sig.Hash(i->c_str(),i->length());
        } else if (sig.HeaderCanonicalization == DKIM_CANON_RELAXED) {
          string sTemp = RelaxHeader(*i);
          sig.Hash(sTemp.c_str(),sTemp.length());
        } else if (sig.HeaderCanonicalization == DKIM_CANON_NOWSP) {
          string sTemp = *i;
          RemoveSWSP(sTemp);
 
          // convert characters before ':' to lower case
          for (char* s = (char*)sTemp.c_str(); *s != '\0' && *s != ':'; s++) {
            if (*s >= 'A' && *s <= 'Z')
              *s += 'a' - 'A';
          }
          sig.Hash(sTemp.c_str(),sTemp.length());
        }
        sig.Hash("\r\n",2);
      }
    }
 
    if (sig.BodyHashData.empty()) {
      // hash CRLF separating headers from body
      sig.Hash("\r\n",2);
    }
 
    if (!m_AllowUnsignedFromHeaders) {
      // make sure the message has no unsigned From headers
      list<string>::reverse_iterator i;
      for (i = HeaderList.rbegin(); i != HeaderList.rend(); ++i) {
        if (_strnicmp(i->c_str(),"From",4) == 0) {
          // skip over whitespace between the header name and :
          const char *s = i->c_str() + 4;
          while (*s == ' ' || *s == '\t')
            s++;
          if (*s == ':') {
            if (find(used.begin(),used.end(),i) == used.end()) {
              // this From header was not signed
              break;
            }
          }
        }
      }
      if (i != HeaderList.rend()) {
        // treat signature as invalid
        sig.Status = DKIM_UNSIGNED_FROM;
        continue;
      }
    }
 
    ValidSigFound = true;
  }
 
  if (!ValidSigFound)
    return DKIM_NO_VALID_SIGNATURES;
 
  return DKIM_SUCCESS;
}
 
 
//
// Strictly parse an unsigned integer.  Don't allow spaces, negative sign,
// 0x prefix, etc.  Values greater than 2^32-1 are capped at 2^32-1
//
bool ParseUnsigned(const char *s, unsigned *result)
{
  unsigned temp = 0, last = 0;
  bool overflowed = false;
 
  do {
    if (*s < '0' || *s > '9')
      return false;        // returns false for an initial '\0'
 
    temp = temp * 10 + (*s - '0');
    if (temp < last)
      overflowed = true;
    last = temp;
 
    s++;
  } while (*s != '\0');
 
  *result = overflowed ? -1 : temp;
  return true;
}
 
 
// 
// ParseDKIMSignature - Parse a DKIM-Signature header field
//
int CDKIMVerify::ParseDKIMSignature(const string& sHeader,SignatureInfo &sig)
{
  // for strtok_r()
  char *saveptr;
 
  // save header for later
  sig.Header = sHeader;
 
  string sValue = sHeader.substr(sHeader.find(':') + 1);
 
  static const char *tags[] = {"v","a","b","d","h","s","c","i","l","q","t","x","bh",NULL};
  char *values[sizeof(tags)/sizeof(tags[0])] = {NULL};
 
  if (!ParseTagValueList((char*) sValue.c_str(),tags,values))
    return DKIM_BAD_SYNTAX;
 
  // check signature version
  if (values[0] == NULL) return DKIM_BAD_SYNTAX;
  
  // signature MUST have a=, b=, d=, h=, s=
  if (values[1] == NULL || values[2] == NULL || values[3] == NULL || values[4] == NULL || values[5] == NULL)
    return DKIM_BAD_SYNTAX;
 
  // algorithm ('a=') can be "rsa-sha1" or "rsa-sha256" or "ed25519"
  if (strcmp(values[1],"rsa-sha1") == 0) {
    sig.m_nHash = DKIM_HASH_SHA1;
  } else if (strcmp(values[1],"rsa-sha256") == 0) {
    sig.m_nHash = DKIM_HASH_SHA256;
  } else if (strcmp(values[1],"ed25519-sha256") == 0) {
    sig.m_nHash = DKIM_HASH_SHA256;
  } else {
    return DKIM_BAD_SYNTAX;    // todo: maybe create a new error code for unknown algorithm
  }
 
  // make sure the signature data is not empty: b=[...]
  unsigned SigDataLen = DecodeBase64(values[2]);
 
  if (SigDataLen == 0)
    return DKIM_BAD_SYNTAX;
 
  sig.SignatureData.assign(values[2],SigDataLen);
 
  // check for body hash in DKIM header: bh=[...];
  unsigned BodyHashLen = DecodeBase64(values[12]);
  if (BodyHashLen == 0) return DKIM_BAD_SYNTAX;
  sig.BodyHashData.assign(values[12],BodyHashLen);
 
  // domain must not be empty
  if (*values[3] == '\0')
    return DKIM_BAD_SYNTAX;
  sig.Domain = values[3];
 
  // signed headers must not be empty (more verification is done later)
  if (*values[4] == '\0')
    return DKIM_BAD_SYNTAX;
 
  // selector must not be empty
  if (*values[5] == '\0')
    return DKIM_BAD_SYNTAX;
  sig.Selector = values[5];
 
  // canonicalization
  if (values[6] == NULL) {
    sig.HeaderCanonicalization = sig.BodyCanonicalization = DKIM_CANON_SIMPLE;
  } else {
    char* slash = strchr(values[6],'/');
    if (slash != NULL)
      *slash = '\0';
 
    if (strcmp(values[6],"simple") == 0)
      sig.HeaderCanonicalization = DKIM_CANON_SIMPLE;
    else if (strcmp(values[6],"relaxed") == 0)
      sig.HeaderCanonicalization = DKIM_CANON_RELAXED;
    else
      return DKIM_BAD_SYNTAX;
 
    if (slash == NULL || strcmp(slash + 1,"simple") == 0)
      sig.BodyCanonicalization = DKIM_CANON_SIMPLE;
    else if (strcmp(slash + 1,"relaxed") == 0)
      sig.BodyCanonicalization = DKIM_CANON_RELAXED;
    else
      return DKIM_BAD_SYNTAX;
  }
 
  // identity
  if (values[7] == NULL) {
    sig.IdentityLocalPart.erase();
    sig.IdentityDomain = sig.Domain;
  } else {
    // quoted-printable decode the value
    DecodeQuotedPrintable(values[7]);
 
    // must have a '@' separating the local part from the domain
    char* at = strchr(values[7],'@');
    if (at == NULL)
      return DKIM_BAD_SYNTAX;
    *at = '\0';
 
    char* ilocalpart = values[7];
    char* idomain = at + 1;
 
    // i= domain must be the same as or a subdomain of the d= domain
    int idomainlen = strlen(idomain);
    int ddomainlen = strlen(values[3]);
 
    // todo: maybe create a new error code for invalid identity domain
    if (idomainlen < ddomainlen)
      return DKIM_BAD_SYNTAX;
    if (_stricmp(idomain + idomainlen - ddomainlen,values[3]) != 0)
      return DKIM_BAD_SYNTAX;
    if (idomainlen > ddomainlen && idomain[idomainlen - ddomainlen - 1] != '.')
      return DKIM_BAD_SYNTAX;
 
    sig.IdentityLocalPart = ilocalpart;
    sig.IdentityDomain = idomain;
  }
 
  // body count
  if (values[8] == NULL || !m_HonorBodyLengthTag) {
    sig.BodyLength = (unsigned) -1;
  } else {
    if (!ParseUnsigned(values[8],&sig.BodyLength))
      return DKIM_BAD_SYNTAX;
  }
 
  // query methods
  if (values[9] != NULL) {
    // make sure "dns" is in the list
    bool HasDNS = false;
    char* s = strtok_r(values[9],":",&saveptr);
    while (s != NULL) {
      if (strncmp(s,"dns",3) == 0 && (s[3] == '\0' || s[3] == '/')) {
        HasDNS = true;
        break;
      }
      s = strtok_r(NULL,": \t",&saveptr);  /* FIXME */
//      s = strtok_r(NULL,":   ",&saveptr);  /* FIXME */
    }
    if (!HasDNS)
      return DKIM_BAD_SYNTAX;    // todo: maybe create a new error code for unknown query method
  }
 
  // signature time
  unsigned SignedTime = -1;
  if (values[10] != NULL) {
    if (!ParseUnsigned(values[10],&SignedTime))
      return DKIM_BAD_SYNTAX;
  }
 
  // expiration time
  if (values[11] == NULL) {
    sig.ExpireTime = (unsigned) -1;   // common trick; feh
  } else {
    if (!ParseUnsigned(values[11],&sig.ExpireTime))
      return DKIM_BAD_SYNTAX;
 
    if (sig.ExpireTime != (unsigned) -1) {
      // the value of x= MUST be greater than the value of t= if both are present
      if (SignedTime != (unsigned) -1 && sig.ExpireTime <= SignedTime)
        return DKIM_BAD_SYNTAX;
 
      // todo: if possible, use the received date/time instead of the current time
      unsigned curtime = time(NULL);
      if (curtime > sig.ExpireTime)
        return DKIM_SIGNATURE_EXPIRED;
    }
  }
 
  // parse the signed headers list
  bool HasFrom = false, HasSubject = false;
  RemoveSWSP(values[4]);      // header names shouldn't have spaces in them so this should be ok...
  char* s = strtok_r(values[4],":",&saveptr);
  while (s != NULL) {
    if (_stricmp(s,"From") == 0)
      HasFrom = true;
    else if (_stricmp(s,"Subject") == 0)
      HasSubject = true;
 
    sig.SignedHeaders.push_back(s);
    s = strtok_r(NULL,":",&saveptr);
  }
 
  if (!HasFrom)
    return DKIM_BAD_SYNTAX;    // todo: maybe create a new error code for h= missing From
  if (m_SubjectIsRequired && !HasSubject)
    return DKIM_BAD_SYNTAX;    // todo: maybe create a new error code for h= missing Subject
 
  return DKIM_SUCCESS;
}
 
// 
// ProcessBody - Process message body data
//
int CDKIMVerify::ProcessBody(char* szBuffer,int nBufLength,bool bEOF)
{
  bool MoreBodyNeeded = false;
 
  for (list<SignatureInfo>::iterator i = Signatures.begin(); i != Signatures.end(); ++i) {
    if (i->Status == DKIM_SUCCESS) {
      if (i->BodyCanonicalization == DKIM_CANON_SIMPLE) {
        if (nBufLength > 0) {
          while (i->EmptyLineCount > 0) {
            i->Hash("\r\n",2,true);
            i->EmptyLineCount--;
          }
          i->Hash(szBuffer,nBufLength,true);
          i->Hash("\r\n",2,true);
        } else {
          i->EmptyLineCount++;
          if (bEOF)
            i->Hash("\r\n",2,true);
        }
      } else if (i->BodyCanonicalization == DKIM_CANON_RELAXED) {
        CompressSWSP(szBuffer, nBufLength);
        if (nBufLength > 0) {
          while (i->EmptyLineCount > 0) {
            i->Hash("\r\n",2,true);
            i->EmptyLineCount--;
          }
          i->Hash(szBuffer,nBufLength,true);
          if (!bEOF)
            i->Hash("\r\n",2,true);
        } else i->EmptyLineCount++;
      } else if (i->BodyCanonicalization == DKIM_CANON_NOWSP) {
        RemoveSWSP(szBuffer,nBufLength);
        i->Hash(szBuffer,nBufLength,true);
      }
 
      if (i->UnverifiedBodyCount == 0)
        MoreBodyNeeded = true;
    }
  }
 
  if (!MoreBodyNeeded)
    return DKIM_FINISHED_BODY;
 
  return DKIM_SUCCESS;
}
 
SelectorInfo::SelectorInfo(const string &sSelector,const string &sDomain) : Domain(sDomain),Selector(sSelector)
{
  AllowSHA1 = true;
  AllowSHA256 = true;
  PublicKey = NULL;
  Testing = false;
  SameDomain = false;
  Status = DKIM_SUCCESS;
}
 
SelectorInfo::~SelectorInfo()
{
  if (PublicKey != NULL) {
    EVP_PKEY_free(PublicKey);
  }
}
 
// 
// Parse - Parse a DKIM selector from DNS data
//
int SelectorInfo::Parse(char* Buffer)
{
  // for strtok_r()
  char *saveptr;
  char *PubKeyBase64; /*- public key Base64 encoded */
  char ed25519PubKey[61];
 
  static const char *tags[] = {"v","g","h","k","p","s","t","n",NULL}; // 0, 1, 2, 3, 4
  char *values[sizeof(tags)/sizeof(tags[0])] = {NULL};
 
  ParseTagValueList(Buffer,tags,values);
   
  //  return DKIM_SELECTOR_INVALID;
  if (values[0] != NULL) {
    // make sure the version is "DKIM1"
    if (strcmp(values[0],"DKIM1") != 0)
      return DKIM_SELECTOR_INVALID;    // todo: maybe create a new error code for unsupported selector version
 
    // make sure v= is the first tag in the response  // todo: maybe don't enforce this, it seems unnecessary
    for (unsigned j = 1; j < sizeof(values)/sizeof(values[0]); j++) {
      if (values[j] != NULL && values[j] < values[0]) {
        return DKIM_SELECTOR_INVALID;
      }
    }
  }
 
  // selector MUST have p= tag
  if (values[4] == NULL)
    return DKIM_SELECTOR_INVALID;
 
  PubKeyBase64 = values[4]; // gotcha
 
  // granularity -- [g= ... ]
  if (values[1] == NULL)
    Granularity = "*";
  else
    Granularity = values[1];
 
  // hash algorithm -- [h=sha1|sha256] (not required)
  if (values[2] == NULL) {
    AllowSHA1 = true;
    AllowSHA256 = true;
  } else {
    // MUST include "sha1" or "sha256"
    char* s = strtok_r(values[2],":",&saveptr);
    while (s != NULL) {
      if (strcmp(s,"sha1") == 0)
        { AllowSHA1 = true; AllowSHA256 = false; }
      else if (strcmp(s,"sha256") == 0)
        { AllowSHA256 = true; AllowSHA1 = false; }
      s = strtok_r(NULL,":",&saveptr);
    }
    if (!(AllowSHA1 || AllowSHA256))
      return DKIM_SELECTOR_INVALID;  // todo: maybe create a new error code for unsupported hash algorithm
  }
 
  // key type -- [k=rsa|ed25519]  (not required)
  if (values[3] != NULL) {
    // key type MUST be "rsa" or "ed25519"
    if (strcmp(values[3],"rsa") != 0 && strcmp(values[3],"ed25519") != 0) // none of either
      return DKIM_SELECTOR_INVALID;
    if (strcmp(values[3],"ed25519") == 0) { 
      AllowSHA1 = false; 
      AllowSHA256 = true; 
      strcpy(ed25519PubKey,"MCowBQYDK2VwAyEA");
      /*
       * rfc8463
       * since Ed25519 public keys are 256 bits long,
       * the base64-encoded key is only 44 octets
       */
      if (strlen(values[4]) > 44)
        return DKIM_SELECTOR_PUBLIC_KEY_INVALID;
      strcat(ed25519PubKey,values[4]);
      PubKeyBase64 = ed25519PubKey;
    } 
  }
 
  // service type -- [s= ...] (not required)
  if (values[5] != NULL) {
    // make sure "*" or "email" is in the list
    bool ServiceTypeMatch = false;
    char* s = strtok_r(values[5],":",&saveptr);
    while (s != NULL) {
      if (strcmp(s, "*") == 0 || strcmp(s,"email") == 0) {
        ServiceTypeMatch = true;
        break;
      }
      s = strtok_r(NULL,":",&saveptr);
    }
    if (!ServiceTypeMatch)
      return DKIM_SELECTOR_INVALID;
  }
 
  // flags -- [t= ...] (not required)
  if (values[6] != NULL) {
    char *s = strtok_r(values[6],":",&saveptr);
    while (s != NULL) {
      if (strcmp(s,"y") == 0) {
        Testing = true;
      } else if (strcmp(s,"s") == 0) {
        SameDomain = true;
      }
      s = strtok_r(NULL,":",&saveptr);
    }
  }
 
  // public key data
  unsigned PublicKeyLen = DecodeBase64(PubKeyBase64);
 
  if (PublicKeyLen == 0) {
    return DKIM_SELECTOR_KEY_REVOKED;  // this error causes the signature to fail
  } else {
    const unsigned char *PublicKeyData = (unsigned char* )PubKeyBase64;  // 0-terminated
 
    EVP_PKEY *pkey = d2i_PUBKEY(NULL,&PublicKeyData,PublicKeyLen);  /* retrieve and return PubKey from data */
 
    if (pkey == NULL)
      return DKIM_SELECTOR_PUBLIC_KEY_INVALID;
 
    // make sure public key is the correct type (we only support rsa & ed25519)
    if ((EVP_PKEY_base_id(pkey) == EVP_PKEY_RSA)  || 
        (EVP_PKEY_base_id(pkey) == EVP_PKEY_RSA2) ||
        (EVP_PKEY_base_id(pkey) == EVP_PKEY_ED25519)) {
      PublicKey = pkey;
    } else {
      EVP_PKEY_free(pkey);
      return DKIM_SELECTOR_PUBLIC_KEY_INVALID;
    }
  }
 
  return DKIM_SUCCESS;
}
 
// 
// GetSelector - Get a DKIM selector for a domain
//
SelectorInfo& CDKIMVerify::GetSelector(const string &sSelector,const string &sDomain)
{
  // see if we already have this selector
  for (list<SelectorInfo>::iterator i = Selectors.begin(); i != Selectors.end(); ++i) {
    if (_stricmp(i->Selector.c_str(),sSelector.c_str()) == 0 && _stricmp(i->Domain.c_str(),sDomain.c_str()) == 0) {
      return *i;
    }
  }
 
  Selectors.push_back(SelectorInfo(sSelector,sDomain));
  SelectorInfo& sel = Selectors.back();
 
  string sFQDN = sSelector;
  sFQDN += "._domainkey.";
  sFQDN += sDomain;
 
  const int BufLen = 1024; 
  char Buffer[BufLen];
 
  int DNSResult;
 
  if (m_pfnSelectorCallback) { 
    DNSResult = m_pfnSelectorCallback(sFQDN.c_str(),Buffer,BufLen);
  } else
    DNSResult = _DNSGetTXT(sFQDN.c_str(),Buffer,BufLen);
 
//  Buffer++; BufLen--;
 
  switch (DNSResult) {
    case -1: case -2: case -3: case -5: sel.Status = DKIM_SELECTOR_DNS_TEMP_FAILURE; break;
    case 0: case -6: sel.Status = DKIM_SELECTOR_DNS_PERM_FAILURE; break;
    default: sel.Status = sel.Parse(Buffer);
 }
 
  return sel;
}
 
// 
// GetDetails - Get DKIM verification details (per signature)
//
int CDKIMVerify::GetDetails(int* nSigCount,DKIMVerifyDetails** pDetails)
{
  Details.clear();
 
  for (list < SignatureInfo>::iterator i = Signatures.begin(); i != Signatures.end(); ++i) {
    DKIMVerifyDetails d;
    d.szSignature = (char* )i->Header.c_str();
    d.szSignatureDomain = (char* )i->Domain.c_str();
    d.szIdentityDomain = (char* )i->IdentityDomain.c_str();
    d.szCanonicalizedData = (char* )i->CanonicalizedData.c_str();
    d.nResult = i->Status;
    Details.push_back(d);
  }
 
  *nSigCount = Details.size();
  *pDetails = (*nSigCount != 0) ? &Details[0] : NULL;
 
  return DKIM_SUCCESS;
}