kevacoin

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Commit Graph

Author	SHA1	Message	Date
Gavin Andresen	8dc206a1e2	Reject non-canonically-encoded sizes The length of vectors, maps, sets, etc are serialized using Write/ReadCompactSize -- which, unfortunately, do not use a unique encoding. So deserializing and then re-serializing a transaction (for example) can give you different bits than you started with. That doesn't cause any problems that we are aware of, but it is exactly the type of subtle mismatch that can lead to exploits. With this pull, reading a non-canonical CompactSize throws an exception, which means nodes will ignore 'tx' or 'block' or other messages that are not properly encoded. Please check my logic... but this change is safe with respect to causing a network split. Old clients that receive non-canonically-encoded transactions or blocks deserialize them into CTransaction/CBlock structures in memory, and then re-serialize them before relaying them to peers. And please check my logic with respect to causing a blockchain split: there are no CompactSize fields in the block header, so the block hash is always canonical. The merkle root in the block header is computed on a vector<CTransaction>, so any non-canonical encoding of the transactions in 'tx' or 'block' messages is erased as they are read into memory by old clients, and does not affect the block hash. And, as noted above, old clients re-serialize (with canonical encoding) 'tx' and 'block' messages before relaying to peers.	11 years ago
Gavin Andresen	87b9931bed	Fix signed/unsigned comparison warnings	12 years ago
Pieter Wuille	4d6144f97f	Compact serialization for variable-length integers Variable-length integers: bytes are a MSB base-128 encoding of the number. The high bit in each byte signifies whether another digit follows. To make the encoding is one-to-one, one is subtracted from all but the last digit. Thus, the byte sequence a[] with length len, where all but the last byte has bit 128 set, encodes the number: (a[len-1] & 0x7F) + sum(i=1..len-1, 128^i((a[len-i-1] & 0x7F)+1)) Properties: Very small (0-127: 1 byte, 128-16511: 2 bytes, 16512-2113663: 3 bytes) * Every integer has exactly one encoding * Encoding does not depend on size of original integer type	12 years ago

Author

SHA1

Message

Date

Gavin Andresen

8dc206a1e2

Reject non-canonically-encoded sizes

The length of vectors, maps, sets, etc are serialized using
Write/ReadCompactSize -- which, unfortunately, do not use a
unique encoding.

So deserializing and then re-serializing a transaction (for example)
can give you different bits than you started with. That doesn't
cause any problems that we are aware of, but it is exactly the type
of subtle mismatch that can lead to exploits.

With this pull, reading a non-canonical CompactSize throws an
exception, which means nodes will ignore 'tx' or 'block' or
other messages that are not properly encoded.

Please check my logic... but this change is safe with respect to
causing a network split. Old clients that receive
non-canonically-encoded transactions or blocks deserialize
them into CTransaction/CBlock structures in memory, and then
re-serialize them before relaying them to peers.

And please check my logic with respect to causing a blockchain
split: there are no CompactSize fields in the block header, so
the block hash is always canonical. The merkle root in the block
header is computed on a vector<CTransaction>, so
any non-canonical encoding of the transactions in 'tx' or 'block'
messages is erased as they are read into memory by old clients,
and does not affect the block hash. And, as noted above, old
clients re-serialize (with canonical encoding) 'tx' and 'block'
messages before relaying to peers.

11 years ago

Gavin Andresen

87b9931bed

Fix signed/unsigned comparison warnings

12 years ago

Pieter Wuille

4d6144f97f

Compact serialization for variable-length integers

Variable-length integers: bytes are a MSB base-128 encoding of the number.
The high bit in each byte signifies whether another digit follows. To make
the encoding is one-to-one, one is subtracted from all but the last digit.
Thus, the byte sequence a[] with length len, where all but the last byte
has bit 128 set, encodes the number:

  (a[len-1] & 0x7F) + sum(i=1..len-1, 128^i*((a[len-i-1] & 0x7F)+1))

Properties:
* Very small (0-127: 1 byte, 128-16511: 2 bytes, 16512-2113663: 3 bytes)
* Every integer has exactly one encoding
* Encoding does not depend on size of original integer type

12 years ago

3 Commits (cd1fc2434ce80f50242e41b5e675f6d0b36045ad)