Add ARC 0032: blockhash & block_height

arc-0032/README.md

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+---
+arc: 0032
+title: Add block_hash and block_height keywords
+authors: [email protected] [email protected]
+discussion: https://github.com/AleoHQ/ARCs/discussions/23
+topic: Application
+status: Draft
+created: 12/2/2022
+---
+
+## Abstract
+
+Currently, it's not possible to get the `block_height` or `blockhash` within an Aleo program. 
+These opcodes would enable Aleo Dapps to take advantage of time without a Time Oracle.
+
+For example, if you have a game like Battleship, a Time Oracle is required to handle the case where one of the players fails to respond. Using `block_height` or `blockhash`, a game could introduce timeouts to handle such edge cases.
+
+
+## Specification
+
+```
+program example.aleo;
+
+record some_record:
+    owner as address.private;
+    gates as u64.private;
+    hash as blockhash.private;
+    height as u64.private;
+
+function create_record:
+    cast self.caller 0u64 blockhash block_height into r0 as some_record.record;
+    output r0 as some_record.record;
+```
+
+We should also considering mirroring Solidity global variables:
+```
+blockhash[block_height]: hash of the given block when blocknumber is one of the 256 most recent blocks; otherwise returns zero
+block.basefee: current block’s base fee (EIP-3198 and EIP-1559)
+block.chainid: current chain id
+block.timestamp: current block timestamp as seconds since unix epoch
+```
+
+## Dependencies
+
+This impacts snarkVM, snarkOS, aleo, & leo repositories. As a new opcode determined from consensus, it will impact all parts of the Aleo ecosystem.
+
+### Backwards Compatibility
+
+Adding new opcodes seems to require a regeneration of the genesis block.
+Existing programs should not be impacted.
+
+
+## Security & Compliance
+
+There should not be any security or compliance considerations. 
+
+DApp developers should not use these variables as a source of randomness as they could be influenced by validators.
+Depending on the usecase, validators may have trouble influencing results if the programs are sufficiently private.
+
+
+## References
+
+Global variables in Solidity: https://docs.soliditylang.org/en/v0.8.17/units-and-global-variables.html