serval-dna/rhizome_crypto.c

/*
Serval Distributed Numbering Architecture (DNA)
Copyright (C) 2010 Paul Gardner-Stephen
 
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.
 
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.
 
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
*/

#include "serval.h"
#include "rhizome.h"
#include <stdlib.h>
#include <ctype.h>

/* Work out the encrypt/decrypt key for the supplied manifest.
   If the manifest is not encrypted, then return NULL.
*/
unsigned char *rhizome_bundle_shared_secret(rhizome_manifest *m)
{
  return NULL;
}

int rhizome_manifest_createid(rhizome_manifest *m)
{
  m->haveSecret=1;
  int r=crypto_sign_edwards25519sha512batch_keypair(m->cryptoSignPublic,m->cryptoSignSecret);
  if (!r) return 0;
  return WHY("Failed to create keypair for manifest ID.");
}

/*
   Return -1 if an error occurs.
   Return 0 if the author's private key is located and the XOR is performed successfully.
   Return 1 if the author's identity is not in the keyring.
   Return 2 if the author's identity is in the keyring but has no rhizome secret.
*/
int rhizome_bk_xor(const unsigned char *authorSid, // binary
		   unsigned char bid[crypto_sign_edwards25519sha512batch_PUBLICKEYBYTES],
		   unsigned char bkin[crypto_sign_edwards25519sha512batch_SECRETKEYBYTES],
		   unsigned char bkout[crypto_sign_edwards25519sha512batch_SECRETKEYBYTES])
{
  IN();
  if (crypto_sign_edwards25519sha512batch_SECRETKEYBYTES > crypto_hash_sha512_BYTES)
    { RETURN(WHY("BK needs to be longer than it can be")); }
  int cn=0,in=0,kp=0;
  if (!keyring_find_sid(keyring,&cn,&in,&kp,authorSid)) {
    if (debug & DEBUG_RHIZOME) DEBUG("identity not in keyring");
    { RETURN(1); }
  }
  kp = keyring_identity_find_keytype(keyring, cn, in, KEYTYPE_RHIZOME);
  if (kp == -1) {
    if (debug & DEBUG_RHIZOME) DEBUG("identity has no Rhizome Secret");
    RETURN(2);
  }
  int rs_len=keyring->contexts[cn]->identities[in]->keypairs[kp]->private_key_len;
  if (rs_len<16||rs_len>1024)
    { RETURN(WHYF("invalid Rhizome Secret: length=%d", rs_len)); }
  unsigned char *rs=keyring->contexts[cn]->identities[in]->keypairs[kp]->private_key;
  int combined_len=rs_len+crypto_sign_edwards25519sha512batch_PUBLICKEYBYTES;
  unsigned char buffer[combined_len];
  bcopy(&rs[0],&buffer[0],rs_len);
  bcopy(&bid[0],&buffer[rs_len],crypto_sign_edwards25519sha512batch_PUBLICKEYBYTES);
  unsigned char hash[crypto_hash_sha512_BYTES];
  crypto_hash_sha512(hash,buffer,combined_len);
  int i;
  for(i = 0; i != crypto_sign_edwards25519sha512batch_SECRETKEYBYTES; ++i)
    bkout[i]=bkin[i]^hash[i];
  bzero(&buffer[0],combined_len);
  bzero(&hash[0],crypto_hash_sha512_BYTES);
  RETURN(0);
}

/* See if the manifest has a BK entry, and if so, use it to obtain the 
   private key for the BID.  Decoding BK's relies on the provision of
   the appropriate SID.

   Return 0 if the private key was extracted, 1 if not.  Return -1 if an error occurs.

   XXX Note that this function is not able to verify that the private key
   is correct, as there is no exposed API in NaCl for calculating the
   public key from a cryptosign private key.  We thus have to trust that
   the supplied SID is correct.

*/
int rhizome_extract_privatekey(rhizome_manifest *m, const unsigned char *authorSid)
{
  IN();
  char *bk = rhizome_manifest_get(m, "BK", NULL, 0);
  if (!bk) { RETURN(WHY("missing BK field")); }
  unsigned char bkBytes[RHIZOME_BUNDLE_KEY_BYTES];
  if (fromhexstr(bkBytes, bk, RHIZOME_BUNDLE_KEY_BYTES) == -1)
    { RETURN(WHYF("invalid BK field: %s", bk)); }
  switch (rhizome_bk_xor(authorSid, m->cryptoSignPublic, bkBytes, m->cryptoSignSecret)) {
    case -1:
      RETURN(WHY("rhizome_bk_xor() failed"));
    case 0:
      RETURN(rhizome_verify_bundle_privatekey(m));
  }
  RETURN(WHYF("Rhizome secret for %s not found. (Have you unlocked the identity?)", alloca_tohex_sid(authorSid)));
}

/*
   Test to see if the given manifest was created (signed) by any unlocked identity currently in the
   keyring.
   Returns -1 if an error occurs, eg, the manifest contains an invalid BK field.
   Return 0 if the manifest's BK field was produced by any currently unlocked SID.
   Returns 1 if the manifest has no BK field.
   Returns 2 otherwise.
 */
int rhizome_is_self_signed(rhizome_manifest *m)
{
  IN();
  char *bk = rhizome_manifest_get(m, "BK", NULL, 0);
  if (!bk) {
    if (debug & DEBUG_RHIZOME) DEBUGF("missing BK field");
    RETURN(1);
  }
  unsigned char bkBytes[RHIZOME_BUNDLE_KEY_BYTES];
  if (fromhexstr(bkBytes, bk, RHIZOME_BUNDLE_KEY_BYTES) == -1)
    { RETURN(WHYF("invalid BK field: %s", bk)); }
  int cn = 0, in = 0, kp = 0;
  for (; keyring_next_identity(keyring, &cn, &in, &kp); ++kp) {
    const unsigned char *authorSid = keyring->contexts[cn]->identities[in]->keypairs[kp]->public_key;
    //if (debug & DEBUG_RHIZOME) DEBUGF("identity %s", alloca_tohex(authorSid, SID_SIZE));
    int rkp = keyring_identity_find_keytype(keyring, cn, in, KEYTYPE_RHIZOME);
    if (rkp != -1) {
      switch (rhizome_bk_xor(authorSid, m->cryptoSignPublic, bkBytes, m->cryptoSignSecret)) {
	case -1:
	  RETURN(WHY("rhizome_bk_xor() failed"));
	case 0:
	  if (rhizome_verify_bundle_privatekey(m) == 0)
	    RETURN(0); // bingo
	  break;
      }
    }
  }
  RETURN(2); // not self signed
}

/* Verify the validity of the manifest's sccret key.
   Return 0 if valid, 1 if not.  Return -1 if an error occurs.
   XXX This is a pretty ugly way to do it, but NaCl offers no API to
   do this cleanly.
 */
int rhizome_verify_bundle_privatekey(rhizome_manifest *m)
{
  IN();
#ifdef HAVE_CRYPTO_SIGN_NACL_GE25519_H
#  include "crypto_sign_edwards25519sha512batch_ref/ge25519.h"
#else
#  ifdef HAVE_KLUDGE_NACL_GE25519_H
#    include "edwards25519sha512batch/ref/ge25519.h"
#  endif
#endif
#ifdef ge25519
  unsigned char *sk=m->cryptoSignSecret;
  unsigned char pk[crypto_sign_edwards25519sha512batch_PUBLICKEYBYTES];
  sc25519 scsk;
  ge25519 gepk;
  sc25519_from32bytes(&scsk,sk);
  ge25519_scalarmult_base(&gepk, &scsk);
  ge25519_pack(pk, &gepk);
  bzero(&scsk,sizeof(scsk));
  if (memcmp(pk, m->cryptoSignPublic, crypto_sign_edwards25519sha512batch_PUBLICKEYBYTES) == 0) {
    m->haveSecret = 1;
    RETURN(0); // valid
  }
  m->haveSecret = 0;
  if (debug & DEBUG_RHIZOME) {
    DEBUGF("  stored public key = %s*", alloca_tohex(m->cryptoSignPublic, 8));
    DEBUGF("computed public key = %s*", alloca_tohex(pk, 8));
  }
  RETURN(1); // invalid
#else //!ge25519
  /* XXX Need to test key by signing and testing signature validity. */
  /* For the time being barf so that the caller does not think we have a validated BK
      when in fact we do not. */
  m->haveSecret=0;
  RETURN(WHY("ge25519 function not available"));
#endif //!ge25519
}

rhizome_signature *rhizome_sign_hash(rhizome_manifest *m, const unsigned char *authorSid)
{
  IN();
  unsigned char *hash=m->manifesthash;
  unsigned char *publicKeyBytes=m->cryptoSignPublic;
  
  if (!m->haveSecret && rhizome_extract_privatekey(m, authorSid)) {
    WHY("Cannot find secret key to sign manifest data.");
    RETURN(NULL);
  }

  /* Signature is formed by running crypto_sign_edwards25519sha512batch() on the 
     hash of the manifest.  The signature actually contains the hash, so to save
     space we cut the hash out of the signature. */
  unsigned char signatureBuffer[crypto_sign_edwards25519sha512batch_BYTES+crypto_hash_sha512_BYTES];
  unsigned long long sigLen=0;
  int mLen=crypto_hash_sha512_BYTES;

  int r=crypto_sign_edwards25519sha512batch(signatureBuffer,&sigLen,
					    &hash[0],mLen,m->cryptoSignSecret);
  if (r) {
    WHY("crypto_sign() failed.");
    RETURN(NULL);
  }

  rhizome_signature *out=calloc(sizeof(rhizome_signature),1);

  /* Here we use knowledge of the internal structure of the signature block
     to remove the hash, since that is implicitly transported, thus reducing the
     actual signature size down to 64 bytes.
     We do then need to add the public key of the signatory on. */
  bcopy(&signatureBuffer[0],&out->signature[1],32);
  bcopy(&signatureBuffer[96],&out->signature[33],32);
  bcopy(&publicKeyBytes[0],&out->signature[65],crypto_sign_edwards25519sha512batch_PUBLICKEYBYTES);
  out->signatureLength=65+crypto_sign_edwards25519sha512batch_PUBLICKEYBYTES;

  out->signature[0]=out->signatureLength;

  RETURN(out);
}

typedef struct manifest_signature_block_cache {
  unsigned char manifest_hash[crypto_hash_sha512_BYTES];
  unsigned char signature_bytes[256];
  int signature_length;
  int signature_valid;
} manifest_signature_block_cache;

#define SIG_CACHE_SIZE 1024
manifest_signature_block_cache sig_cache[SIG_CACHE_SIZE];

int rhizome_manifest_lookup_signature_validity(unsigned char *hash,unsigned char *sig,int sig_len)
{
  IN();
  unsigned int slot=0;
  int i;

  for(i=0;i<crypto_hash_sha512_BYTES;i++) {
    slot=(slot<<1)+(slot&0x80000000?1:0);
    slot+=hash[i];
  }
  for(i=0;i<sig_len;i++) {
    slot=(slot<<1)+(slot&0x80000000?1:0);
    slot+=sig[i];
  }
  slot%=SIG_CACHE_SIZE;

  int replace=0;
  if (sig_cache[slot].signature_length!=sig_len) replace=1;
  for(i=0;i<crypto_hash_sha512_BYTES;i++)
    if (hash[i]!=sig_cache[i].manifest_hash[i]) { replace=1; break; }
  for(i=0;i<sig_len;i++)
    if (sig[i]!=sig_cache[i].signature_bytes[i]) { replace=1; break; }

  if (replace) {
    for(i=0;i<crypto_hash_sha512_BYTES;i++)
      sig_cache[i].manifest_hash[i]=hash[i];
    for(i=0;i<sig_len;i++)
      sig_cache[i].signature_bytes[i]=sig[i];
    sig_cache[i].signature_length=sig_len;

    unsigned char sigBuf[256];
    unsigned char verifyBuf[256];
    unsigned char publicKey[256];

    /* Reconstitute signature by putting manifest hash between the two
       32-byte halves */
    bcopy(&sig[0],&sigBuf[0],32);
    bcopy(hash,&sigBuf[32],crypto_hash_sha512_BYTES);
    bcopy(&sig[32],&sigBuf[96],32);

    /* Get public key of signatory */
    bcopy(&sig[64],&publicKey[0],crypto_sign_edwards25519sha512batch_PUBLICKEYBYTES);

    unsigned long long mlen=0;
    sig_cache[i].signature_valid=
      crypto_sign_edwards25519sha512batch_open(verifyBuf,&mlen,&sigBuf[0],128,
					       publicKey)
      ? -1 : 0;
  }
  RETURN(sig_cache[i].signature_valid);
}

int rhizome_manifest_extract_signature(rhizome_manifest *m,int *ofs)
{
  IN();
  if (!m) { RETURN(WHY("NULL pointer passed in as manifest")); }

  if ((*ofs)>=m->manifest_all_bytes) { RETURN(0); }

  int len=m->manifestdata[*ofs];
  if (!len) { 
    (*ofs)=m->manifest_bytes;
    m->errors++;
    RETURN(WHY("Zero byte signature blocks are not allowed, assuming signature section corrupt."));
  }

  /* Each signature type is required to have a different length to detect it.
     At present only crypto_sign_edwards25519sha512batch() signatures are
     supported. */
  int r;
  if (m->sig_count<MAX_MANIFEST_VARS)
    switch(len) 
      {
      case 0x61: /* crypto_sign_edwards25519sha512batch() */
	/* Reconstitute signature block */
	r=rhizome_manifest_lookup_signature_validity
	  (m->manifesthash,&m->manifestdata[(*ofs)+1],96);
#ifdef DEPRECATED
	unsigned char sigBuf[256];
	unsigned char verifyBuf[256];
	unsigned char publicKey[256];
	bcopy(&m->manifestdata[(*ofs)+1],&sigBuf[0],32);
	bcopy(&m->manifesthash[0],&sigBuf[32],crypto_hash_sha512_BYTES);
	bcopy(&m->manifestdata[(*ofs)+1+32],&sigBuf[96],32);
	/* Get public key of signatory */
	bcopy(&m->manifestdata[(*ofs)+1+64],&publicKey[0],crypto_sign_edwards25519sha512batch_PUBLICKEYBYTES);
	unsigned long long mlen=0;
	int r=crypto_sign_edwards25519sha512batch_open(verifyBuf,&mlen,&sigBuf[0],128, publicKey);
#endif
	if (r) {
	  (*ofs)+=len;
	  m->errors++;
	  RETURN(WHY("Error in signature block (verification failed)."));
	} else {
	  /* Signature block passes, so add to list of signatures */
	  m->signatureTypes[m->sig_count]=len;
	  m->signatories[m->sig_count]
	    =malloc(crypto_sign_edwards25519sha512batch_PUBLICKEYBYTES);
	  if(!m->signatories[m->sig_count]) {
	    (*ofs)+=len;
	    RETURN(WHY("malloc() failed when reading signature block"));
	  }
	  bcopy(&m->manifestdata[(*ofs)+1+64],m->signatories[m->sig_count],
		crypto_sign_edwards25519sha512batch_PUBLICKEYBYTES);
	  m->sig_count++;
	  if (debug&DEBUG_RHIZOME) DEBUG("Signature passed.");
	}
	break;
      default:
	(*ofs)+=len;
	m->errors++;
	RETURN(WHY("Encountered illegal or malformed signature block"));
      }
  else
    {
      (*ofs)+=len;
      WHY("Too many signature blocks in manifest.");
      m->errors++;
    }

  (*ofs)+=len;
  RETURN(0);
}