Polkadot Extrinsic format

Polkadot Extrinsic format aka Transaction format

This is out of date. Please see https://github.com/paritytech/substrate/pull/195 for more information.

Polkadot Extrinsics are currently a bare binary format. All numerics are in LE format. It is the concatenation of these fields:

• 4 bytes: 32-bit length of the extrinsic data, not including these 4 bytes.
• 32 bytes: 256-bit Ed25519 public key of the sender.
• 8 bytes: 64-bit transaction index of the sender.
• At least 2 bytes: Runtime call end-point descriptor. See the runtime for more information.
• 64 bytes: 512-bit Ed25519 signature over the previous 3 fields, signed by the sender. Note that the 4-byte length field is not included.

Example:

0x
..000000
d172a74cda4c865912c32ba0a80a57ae69abae410e5ccb59dee84e2f4432db4f
0000000000000000
0200
d7568e5f0a7eda67a82691ff379ac4bba4f9c9b859fe779b5d46363b61ad2db9
2a00000000000000
................................................................................................................................