add crypto primitives

docs/crypto.rst

@@ -0,0 +1,25 @@
+.. _crypto:
+
+Cryptographic Primitives
+========================
+
+Algorand Smart Contracts support 4 cryptographic primitives, including 3 cryptographic
+hash functions and 1 digital signature verification. Each of these cryptographic
+primitives is associated with a cost, which is a number indicating its relative performance
+overhead comparing with simple teal operations such as addition and substraction.
+All TEAL opcodes except crypto primitives have cost `1`.
+Below is how you express cryptographic primitives in PyTeal:
+
+
+=============================== ========= ================================================================================ 
+Operator                        Cost      Description
+=============================== ========= ================================================================================
+:code:`Sha256(e)`               `7`       `SHA-256` hash function, produces 32 bytes
+:code:`Keccak256(e)`            `26`      `Keccak-256` hash funciton, produces 32 bytes
+:code:`Sha512_256(e)`           `9`       `SHA512-256` hash function, produces 32 bytes
+:code:`Ed25519verify(d, s, p)`  `1900`    `1` if :code:`s` is the signature of :code:`d` signed by :code:`p` (PK), else `0`
+=============================== ========= ================================================================================
+
+These cryptographic primitives cover the most used ones in blockchains and cryptocurrencies. For example, Bitcoin uses `SHA-256` for creating Bitcoin addresses;
+Alogrand uses `ed25519` signature scheme for authorization and uses `SHA512-256` hash function for
+creating contract account addresses from TEAL bytecode.

docs/index.rst

@@ -36,6 +36,7 @@ PyTeal **hasn't been security audited**. Use it at your own risk.
    arithmetic_expression
    accessing_transaction_field
    atomic_transfer
+   crypto
    control_structures
    API
    using_pyteal_with_sdk