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# Algorand Specifications

For a _player_ with their _participation keys_ registered on the Ledger (and hosted
on an Algorand node), a set of _ephemeral sub-keys_ is created.

An _ephemeral sub-key_ is a key pair that produces one-time signature
for messages. It **MUST** be deleted after use to ensure forward security.
Algorand’s ephemeral subkeys use [Ed25519 public-key signature system](https://ed25519.cr.yp.to/).

> For further details, refer to the Cryptography primitives [specification](https://specs.algorand.co/crypto/crypto).

Algorand uses a two-level ephemeral signature scheme.
Instead of signing voting messages directly, Algorand accounts use their
registered _voting keys_ to sign an intermediate ephemeral sub-key.

This intermediate ephemeral sub-key signs a batch of leaf-level ephemeral
sub-keys. Hence, each intermediate ephemeral sub-key is associated with a
batch number (BatchBatch), and each leaf ephemeral sub-key is associated with
both a batch number (of its parent key) and an offset (OffsetOffset, denotes its offset
within a BatchBatch). An [agreement voting message](https://specs.algorand.co/abft/abft-messages-votes)
is signed hierarchically:

```text

Voting Keys Root Key
└── Batch Sub-Key
    └── Leaf Sub-Key
        └── Agreement Voting Message
```

> Further details on this process in the [One-time Signature subsection](https://specs.algorand.co/keys/keys-one-time).

Each leaf-level ephemeral sub-key is used for voting on a single agreement round,
and will be deleted afterward. Once a batch of leaf-level ephemeral sub-keys run out,
a new batch is generated. Algorand allows users to set the number of leaf-level ephemeral
sub-key per batch, KeyDilutionKeyDilution.

> The default KeyDilutionKeyDilution value is 10,00010,000.

An Algorand account can change its KeyDilutionKeyDilution in the _participation keys_
_registration_.

> For further details about the structure of a _participation keys_ registration
> (`keyreg`) transaction, refer to the Ledger [specification](https://specs.algorand.co/ledger/ledger-overview).

The following diagram shows the tree structure of the voting signature scheme:

```

One-Time Signature container

Batch Signer 1

Batch Signer 2

...

Batch Signer N

Batch 1 Key 1

Batch 1 Key 2

...

Batch 1 Key N
```