## Introduction#

Rather than storing a single amount (like BTC), an ergo eutxo box has some registers to store arbitrary values, like its native tokens.

Addresses are short strings that correspond to specific scripts and are used to protect a box

So, each box has an ERG amount and may or may not have a bunch of {tokenid, token amount} pairs, all in the UTXO model.

Unlike account-based models like eth, ergo tokens are native and are not smart contracts.

## Base58#

Unlike a (hex-encoded) binary representation of a script, an Ergo address use a Base58-encoding and therefore has some advantageous characteristics which the binary representation does not offer:

• We can quickly check the integrity of an address via an integrated checksum (a "small-sized datum derived from a block of digital data to detect errors that may have been introduced during its transmission or storage", according to Wikipedia).
• A prefix of the Address shows you the network and address type. In particular, the network prefix prevents you from mistakenly sending mainnet tokens to the testnet Address.
• The Address uses an encoding (namely, Base58, as mentioned) that avoids similarly-looking characters and is friendly to double-clicking and line-breaking in emails.
• An address encodes network type, address type, checksum, and enough information to correspond with particular scripts.

Let's look at the prefix byte, which contains information about the network and address types:

## Possible Types#

Possible network types are:

• Mainnet - 0x00
• Testnet - 0x10

Address types are (semantics described below):

• 0x01 - Pay-to-PublicKey(P2PK) address
• 0x02 - Pay-to-Script-Hash(P2SH)
• 0x03 - Pay-to-Script(P2S)

For an address type, we form content bytes as follows:

• P2PK - serialized (compressed) public key
• P2SH - first 192 bits of the Blake2b256 hash of serialized script bytes
• P2S - serialized script (this is where mining rewards go!)

For example,

• Sending 10 ERG to a P2PK address usually means that a corresponding transaction will contain a box in which 10 Ergs are locked by a public key encoded in the P2PK Address.
• Similarly, in the case of a P2S address, the box will be locked by a script encoded in the Address.
• In the most complicated case of a P2SH script, the box will be protected by a special predefined script that takes the first 192 bits of Blake2b256 hash value for a script shown by an input spending the box.

Here are some examples of the various types of addresses you'll see on the testnet:

• P2PK (3WvsT2Gm4EpsM9Pg18PdY6XyhNNMqXDsvJTbbf6ihLvAmSb7u5RN)
• P2SH (rbcrmKEYduUvADj9Ts3dSVSG27h54pgrq5fPuwB)
• P2S (Ms7smJwLGbUAjuWQ)

And here is how what they look like on the mainnet:

• P2PK (9fRAWhdxEsTcdb8PhGNrZfwqa65zfkuYHAMmkQLcic1gdLSV5vA)
• P2SH (8UApt8czfFVuTgQmMwtsRBZ4nfWquNiSwCWUjMg)
• P2S (4MQyML64GnzMxZgm, BxKBaHkvrTvLZrDcZjcsxsF7aSsrN73ijeFZXtbj4CXZHHcvBtqSxQ)

Note: P2S can start with any number, D, M, or any other of base58. 9 is always a P2PK address on the mainnet.

## Summary#

• Prefix byte = network type + address type
• (for example, P2S script on the testnet starts with 0x13 before Base58)
• checksum = leftmost_4_bytes (blake2b256 (prefix byte || content bytes))
• address = prefix byte || content bytes || checksum

ergo-simple-addresses contains few zero-dependencies Java-friendly utils for working with addresses. The Integration Guide for Exchanges may also be relevant. There is also a simple method in Fleet.

• P2S has no limit since it is the serialized script.
• P2SH is 192 bits since it is the "first 192 bits of the Blake2b256 hash of serialized script bytes."
• P2PK length is fixed. You can use the linked class to validate an address (it gives a runtime exception when created from an invalid string).

In P2S, everyone can see the script; in P2SH, the script will be known when it will be spent.

P2SH has 0x12 at the beginning, and P2S has 0x13 on testnet and 0x02 and 0x03 on mainnet accordingly (note that in hex, you can see that, but in base58, it can change to anything).

As you can see

88dhgzEuTXaRxf1rbqBRZ6Zbw9iigdB4PCdjyFKLrk22gnmjKcxZBe53vqJVetRa4tTNF9oowQWPp2c6

equals

03 10 02 04 a0 0b 08 cd 02 a1 f5 67 16 cb 8d f4 fe b9 37 14 37 90 4b 91 25 b8 2d b9 39 23 8c d7 d9 48 78 6d b3 3d e3 13 9f ea 02 d1 92 a3 9a 8c c7 a7 01 73 00 73 01 8c 23 55 af

## Resources#

• Ergo Vision | A wallet visualization tool to be used for investigating transactions and addresses