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gpg: Factor common code out of the AEAD decryption function.

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* g10/decrypt-data.c (aead_underflow): Factor reading and checking
code code out to ...
(fill_buffer, aead_checktag): new functions.
--

Here is a simple test script to check against a set of encrypted files
with naming convention like "symenc-aead-eax-c6-56.asc"

# ------------------------ >8 ------------------------
set -e
GPG=../g10/gpg
for file in "$@"; do
  echo "${file##*/}" | ( IFS=- read dummy1 dummy2 mode cbyte len rest
  len="${len%.*}"
  cbyte="${cbyte#c}"
  [ "$dummy1" != "symenc" -o "$dummy2" != "aead" ] && continue
  echo "checking mode=$mode chunkbyte=$cbyte length=$len"
  if ! $GPG --no-options --rfc4880bis --batch --passphrase "abc" \
             -d < $file >tmp.plain 2>/dev/null; then
      echo "Decryption failed for $file" >&2
      exit 2
  fi
  plainlen=$(wc -c <tmp.plain)
  if [ $plainlen -ne $len ]; then
      echo "Plaintext length mismatch for $file (want=$len have=$plainlen)" >&2
      exit 2
  fi

  )
done
echo "all files are okay" >&2
# ------------------------ 8< ------------------------

Signed-off-by: Werner Koch <wk@gnupg.org>
This commit is contained in:
Werner Koch 2018-02-27 19:50:54 +01:00
parent b703ba725d
commit ad989373f1
No known key found for this signature in database
GPG Key ID: E3FDFF218E45B72B
1 changed files with 77 additions and 96 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

173
g10/decrypt-data.c
View File

@ -192,6 +192,28 @@ aead_set_ad (decode_filter_ctx_t dfx, int final)
}
/* Helper to check the 16 byte tag in TAGBUF. The FINAL flag is only
* for debug messages. */
static gpg_error_t
aead_checktag (decode_filter_ctx_t dfx, int final, const void *tagbuf)
{
gpg_error_t err;
if (DBG_FILTER)
log_printhex (tagbuf, 16, "tag:");
err = gcry_cipher_checktag (dfx->cipher_hd, tagbuf, 16);
if (err)
{
log_error ("gcry_cipher_checktag%s failed: %s\n",
final? " (final)":"", gpg_strerror (err));
return err;
}
if (DBG_FILTER)
log_debug ("%stag is valid\n", final?"final ":"");
return 0;
}
/****************
* Decrypt the data, specified by ED with the key DEK.
*/
@ -531,6 +553,49 @@ decrypt_data (ctrl_t ctrl, void *procctx, PKT_encrypted *ed, DEK *dek)
}
/* Fill BUFFER with up to NBYTES-OFFSET from STREAM utilizing
* information from the context DFX. Returns the new offset which is
* the number of bytes read plus the original offset. On EOF the
* respective flag in DFX is set. */
static size_t
fill_buffer (decode_filter_ctx_t dfx, iobuf_t stream,
byte *buffer, size_t nbytes, size_t offset)
{
size_t nread = offset;
int c;
if (dfx->partial)
{
for (; nread < nbytes; nread++ )
{
if ((c = iobuf_get (stream)) == -1)
{
dfx->eof_seen = 1; /* Normal EOF. */
break;
}
buffer[nread] = c;
}
}
else
{
for (; nread < nbytes && dfx->length; nread++, dfx->length--)
{
c = iobuf_get (stream);
if (c == -1)
{
dfx->eof_seen = 3; /* Premature EOF. */
break;
}
buffer[nread] = c;
}
if (!dfx->length)
dfx->eof_seen = 1; /* Normal EOF. */
}
return nread;
}
/* The core of the AEAD decryption. This is the underflow function of
* the aead_decode_filter. */
static gpg_error_t
@ -542,7 +607,6 @@ aead_underflow (decode_filter_ctx_t dfx, iobuf_t a, byte *buf, size_t *ret_len)
size_t off = 0; /* The offset into the buffer. */
size_t len; /* The current number of bytes in BUF+OFF. */
int last_chunk_done = 0; /* Flag that we processed the last chunk. */
int c;
log_assert (size > 48); /* Our code requires at least this size. */
@ -560,39 +624,12 @@ aead_underflow (decode_filter_ctx_t dfx, iobuf_t a, byte *buf, size_t *ret_len)
* chunksize. After the last data byte from the last chunk 32 more
* bytes are expected for the last chunk's tag and the following
* final chunk's tag. To detect the EOF we need to try reading at least
* one further byte; however we try to ready 16 extra bytes to avoid
* one further byte; however we try to read 16 extra bytes to avoid
* single byte reads in some lower layers. The outcome is that we
* have up to 48 extra extra octets which we will later put into the
* holdback buffer for the next invocation (which handles the EOF
* case). */
if (dfx->partial)
{
for (; len < size; len++ )
{
if ((c = iobuf_get (a)) == -1)
{
dfx->eof_seen = 1; /* Normal EOF. */
break;
}
buf[len] = c;
}
}
else
{
for (; len < size && dfx->length; len++, dfx->length--)
{
c = iobuf_get (a);
if (c == -1)
{
dfx->eof_seen = 3; /* Premature EOF. */
break;
}
buf[len] = c;
}
if (!dfx->length)
dfx->eof_seen = 1; /* Normal EOF. */
}
len = fill_buffer (dfx, a, buf, size, len);
if (len < 32)
{
/* Not enough data for the last two tags. */
@ -673,47 +710,19 @@ aead_underflow (decode_filter_ctx_t dfx, iobuf_t a, byte *buf, size_t *ret_len)
err = gpg_error (GPG_ERR_TRUNCATED);
goto leave;
}
len = 0;
last_chunk_done = 1;
}
else
{
len = dfx->holdbacklen;
if (dfx->partial)
{
for (; len < 48; len++ )
{
if ((c = iobuf_get (a)) == -1)
{
dfx->eof_seen = 1; /* Normal EOF. */
break;
}
dfx->holdback[len] = c;
}
}
else
{
for (; len < 48 && dfx->length; len++, dfx->length--)
{
c = iobuf_get (a);
if (c == -1)
{
dfx->eof_seen = 3; /* Premature EOF. */
break;
}
dfx->holdback[len] = c;
}
if (!dfx->length)
dfx->eof_seen = 1; /* Normal EOF. */
}
if (len < 32)
len = 0;
dfx->holdbacklen = fill_buffer (dfx, a, dfx->holdback, 48,
dfx->holdbacklen);
if (dfx->holdbacklen < 32)
{
/* Not enough data for the last two tags. */
err = gpg_error (GPG_ERR_TRUNCATED);
goto leave;
}
dfx->holdbacklen = len;
len = 0;
}
}
else /* We already have the full tag. */
@ -723,18 +732,9 @@ aead_underflow (decode_filter_ctx_t dfx, iobuf_t a, byte *buf, size_t *ret_len)
memmove (buf + off, buf + off + 16, len - 16);
len -= 16;
}
if (DBG_CRYPTO)
log_printhex (tagbuf, 16, "tag:");
err = gcry_cipher_checktag (dfx->cipher_hd, tagbuf, 16);
err = aead_checktag (dfx, 0, tagbuf);
if (err)
{
if (DBG_FILTER)
log_debug ("gcry_cipher_checktag failed (1): %s\n",
gpg_strerror (err));
goto leave;
}
if (DBG_FILTER)
log_debug ("tag is valid\n");
goto leave;
/* Prepare a new chunk. */
if (!last_chunk_done)
@ -783,18 +783,9 @@ aead_underflow (decode_filter_ctx_t dfx, iobuf_t a, byte *buf, size_t *ret_len)
if (!last_chunk_done)
{
log_assert (dfx->holdbacklen >= 32);
if (DBG_FILTER)
log_printhex (dfx->holdback, 16, "tag:");
err = gcry_cipher_checktag (dfx->cipher_hd, dfx->holdback, 16);
err = aead_checktag (dfx, 0, dfx->holdback);
if (err)
{
log_error ("gcry_cipher_checktag failed (2): %s\n",
gpg_strerror (err));
goto leave;
}
if (DBG_FILTER)
log_debug ("tag is valid\n");
goto leave;
}
/* Check the final chunk. */
@ -815,19 +806,9 @@ aead_underflow (decode_filter_ctx_t dfx, iobuf_t a, byte *buf, size_t *ret_len)
gpg_strerror (err));
goto leave;
}
if (DBG_CRYPTO)
log_printhex (dfx->holdback+(last_chunk_done?0:16), 16, "tag:");
err = gcry_cipher_checktag (dfx->cipher_hd,
dfx->holdback+(last_chunk_done?0:16), 16);
err = aead_checktag (dfx, 1, dfx->holdback+(last_chunk_done?0:16));
if (err)
{
if (DBG_FILTER)
log_debug ("gcry_cipher_checktag failed (final): %s\n",
gpg_strerror (err));
goto leave;
}
if (DBG_FILTER)
log_debug ("final tag is valid\n");
goto leave;
err = gpg_error (GPG_ERR_EOF);
}