Tendermint uses the proto3 derivative Amino for all data structures. Think of Amino as an object-oriented proto3 with native JSON support. The goal of the Amino encoding protocol is to bring parity between application logic objects and persistence objects.
Please see the Amino specification for more details.
Notably, every object that satisfies an interface (eg. a particular kind of p2p message, or a particular kind of pubkey) is registered with a global name, the hash of which is included in the object's encoding as the so-called "prefix bytes".
We define the func AminoEncode(obj interface{}) []byte function to take an
arbitrary object and return the Amino encoded bytes.
The encoding of a byte array is simply the raw-bytes prefixed with the length of
the array as a UVarint (what proto calls a Varint).
For details on varints, see the protobuf spec.
For example, the byte-array [0xA, 0xB] would be encoded as 0x020A0B,
while a byte-array containing 300 entires beginning with [0xA, 0xB, ...] would
be encoded as 0xAC020A0B... where 0xAC02 is the UVarint encoding of 300.
Tendermint uses Amino to distinguish between different types of private keys, public keys, and signatures. Additionally, for each public key, Tendermint defines an Address function that can be used as a more compact identifier in place of the public key. Here we list the concrete types, their names, and prefix bytes for public keys and signatures, as well as the address schemes for each PubKey. Note for brevity we don't include details of the private keys beyond their type and name, as they can be derived the same way as the others using Amino.
All registered objects are encoded by Amino using a 4-byte PrefixBytes that uniquely identifies the object and includes information about its underlying type. For details on how PrefixBytes are computed, see the Amino spec.
In what follows, we provide the type names and prefix bytes directly.
Notice that when encoding byte-arrays, the length of the byte-array is appended
to the PrefixBytes. Thus the encoding of a byte array becomes <PrefixBytes> <Length> <ByteArray>. In other words, to encode any type listed below you do not need to be
familiar with amino encoding.
You can simply use below table and concatenate Prefix || Length (of raw bytes) || raw bytes
( while || stands for byte concatenation here).
| Type | Name | Prefix | Length | Notes |
|---|---|---|---|---|
| PubKeyEd25519 | tendermint/PubKeyEd25519 | 0x1624DE64 | 0x20 | |
| PubKeySecp256k1 | tendermint/PubKeySecp256k1 | 0xEB5AE987 | 0x21 | |
| PrivKeyEd25519 | tendermint/PrivKeyEd25519 | 0xA3288910 | 0x40 | |
| PrivKeySecp256k1 | tendermint/PrivKeySecp256k1 | 0xE1B0F79B | 0x20 | |
| PubKeyMultisigThreshold | tendermint/PubKeyMultisigThreshold | 0x22C1F7E2 | variable |
For example, the 33-byte (or 0x21-byte in hex) Secp256k1 pubkey
020BD40F225A57ED383B440CF073BC5539D0341F5767D2BF2D78406D00475A2EE9
would be encoded as
EB5AE98721020BD40F225A57ED383B440CF073BC5539D0341F5767D2BF2D78406D00475A2EE9
Addresses for each public key types are computed as follows:
First 20-bytes of the SHA256 hash of the raw 32-byte public key:
address = SHA256(pubkey)[:20]
NOTE: before v0.22.0, this was the RIPEMD160 of the Amino encoded public key.
RIPEMD160 hash of the SHA256 hash of the OpenSSL compressed public key:
address = RIPEMD160(SHA256(pubkey))
This is the same as Bitcoin.
The BitArray is used in block headers and some consensus messages to signal
whether or not something was done by each validator. BitArray is represented
with a struct containing the number of bits (Bits) and the bit-array itself
encoded in base64 (Elems).
type BitArray struct {
Bits int
Elems []uint64
}This type is easily encoded directly by Amino.
Note BitArray receives a special JSON encoding in the form of x and _
representing 1 and 0. Ie. the BitArray 10110 would be JSON encoded as
"x_xx_"
Part is used to break up blocks into pieces that can be gossiped in parallel and securely verified using a Merkle tree of the parts.
Part contains the index of the part in the larger set (Index), the actual
underlying data of the part (Bytes), and a simple Merkle proof that the part is contained in
the larger set (Proof).
type Part struct {
Index int
Bytes byte[]
Proof byte[]
}Encode an object using Amino and slice it into parts.
func MakeParts(obj interface{}, partSize int) []PartFor an overview of Merkle trees, see wikipedia
A Simple Tree is a simple compact binary tree for a static list of items. Simple Merkle trees are used in numerous places in Tendermint to compute a cryptographic digest of a data structure. In a Simple Tree, the transactions and validation signatures of a block are hashed using this simple merkle tree logic.
If the number of items is not a power of two, the tree will not be full and some leaf nodes will be at different levels. Simple Tree tries to keep both sides of the tree the same size, but the left side may be one greater, for example:
Simple Tree with 6 items Simple Tree with 7 items
* *
/ \ / \
/ \ / \
/ \ / \
/ \ / \
* * * *
/ \ / \ / \ / \
/ \ / \ / \ / \
/ \ / \ / \ / \
* h2 * h5 * * * h6
/ \ / \ / \ / \ / \
h0 h1 h3 h4 h0 h1 h2 h3 h4 h5
Tendermint always uses the TMHASH hash function, which is equivalent to
SHA256:
func TMHASH(bz []byte) []byte {
return SHA256(bz)
}
The function SimpleMerkleRoot is a simple recursive function defined as follows:
func SimpleMerkleRoot(hashes [][]byte) []byte{
switch len(hashes) {
case 0:
return nil
case 1:
return hashes[0]
default:
left := SimpleMerkleRoot(hashes[:(len(hashes)+1)/2])
right := SimpleMerkleRoot(hashes[(len(hashes)+1)/2:])
return SimpleConcatHash(left, right)
}
}
func SimpleConcatHash(left, right []byte) []byte{
left = encodeByteSlice(left)
right = encodeByteSlice(right)
return TMHASH(append(left, right))
}Note that the leaves are Amino encoded as byte-arrays (ie. simple Uvarint length prefix) before being concatenated together and hashed.
Note: we will abuse notion and invoke SimpleMerkleRoot with arguments of type struct or type []struct.
For struct arguments, we compute a [][]byte containing the hash of each
field in the struct, in the same order the fields appear in the struct.
For []struct arguments, we compute a [][]byte by hashing the individual struct elements.
Proof that a leaf is in a Merkle tree consists of a simple structure:
type SimpleProof struct {
Aunts [][]byte
}
Which is verified using the following:
func (proof SimpleProof) Verify(index, total int, leafHash, rootHash []byte) bool {
computedHash := computeHashFromAunts(index, total, leafHash, proof.Aunts)
return computedHash == rootHash
}
func computeHashFromAunts(index, total int, leafHash []byte, innerHashes [][]byte) []byte{
assert(index < total && index >= 0 && total > 0)
if total == 1{
assert(len(proof.Aunts) == 0)
return leafHash
}
assert(len(innerHashes) > 0)
numLeft := (total + 1) / 2
if index < numLeft {
leftHash := computeHashFromAunts(index, numLeft, leafHash, innerHashes[:len(innerHashes)-1])
assert(leftHash != nil)
return SimpleHashFromTwoHashes(leftHash, innerHashes[len(innerHashes)-1])
}
rightHash := computeHashFromAunts(index-numLeft, total-numLeft, leafHash, innerHashes[:len(innerHashes)-1])
assert(rightHash != nil)
return SimpleHashFromTwoHashes(innerHashes[len(innerHashes)-1], rightHash)
}
The Simple Tree is used to merkelize a list of items, so to merkelize a
(short) dictionary of key-value pairs, encode the dictionary as an
ordered list of KVPair structs. The block hash is such a hash
derived from all the fields of the block Header. The state hash is
similarly derived.
Because Tendermint only uses a Simple Merkle Tree, application developers are expect to use their own Merkle tree in their applications. For example, the IAVL+ Tree - an immutable self-balancing binary tree for persisting application state is used by the Cosmos SDK
Amino also supports JSON encoding - registered types are simply encoded as:
{
"type": "<amino type name>",
"value": <JSON>
}
For instance, an ED25519 PubKey would look like:
{
"type": "tendermint/PubKeyEd25519",
"value": "uZ4h63OFWuQ36ZZ4Bd6NF+/w9fWUwrOncrQsackrsTk="
}
Where the "value" is the base64 encoding of the raw pubkey bytes, and the
"type" is the amino name for Ed25519 pubkeys.
Signed messages (eg. votes, proposals) in the consensus are encoded using Amino.
When signing, the elements of a message are re-ordered so the fixed-length fields
are first, making it easy to quickly check the type, height, and round.
The ChainID is also appended to the end.
We call this encoding the SignBytes. For instance, SignBytes for a vote is the Amino encoding of the following struct:
type CanonicalVote struct {
Type byte
Height int64 `binary:"fixed64"`
Round int64 `binary:"fixed64"`
Timestamp time.Time
BlockID CanonicalBlockID
ChainID string
}The field ordering and the fixed sized encoding for the first three fields is optimized to ease parsing of SignBytes in HSMs. It creates fixed offsets for relevant fields that need to be read in this context. See #1622 for more details.