Add keccak256 hash function

cairo/ethereum/crypto/hash.cairo

@@ -1,3 +1,20 @@
-from ethereum.base_types import Bytes32
+from ethereum.base_types import Bytes32, Bytes, Uint256
+from src.utils.bytes import bytes_to_bytes8_little_endian
+from starkware.cairo.common.builtin_keccak.keccak import keccak_bigend
+from starkware.cairo.common.cairo_builtins import BitwiseBuiltin, KeccakBuiltin
+from starkware.cairo.common.alloc import alloc
 
 using Hash32 = Bytes32;
+
+func keccak256{range_check_ptr, bitwise_ptr: BitwiseBuiltin*, keccak_ptr: KeccakBuiltin*}(
+    buffer: Bytes
+) -> Hash32 {
+    alloc_locals;
+    let (local dst: felt*) = alloc();
+    bytes_to_bytes8_little_endian(dst, buffer.value.len, buffer.value.data);
+
+    let (code_hash) = keccak_bigend(dst, buffer.value.len);
+    tempvar value = new Uint256(low=code_hash.low, high=code_hash.high);
+    tempvar hash = Hash32(value=value);
+    return hash;
+}

cairo/tests/ethereum/crypto/test_hash.cairo

@@ -0,0 +1,11 @@
+from ethereum.crypto.hash import keccak256, Hash32
+from ethereum.base_types import Bytes
+from starkware.cairo.common.cairo_builtins import KeccakBuiltin, BitwiseBuiltin
+
+func test_keccak256{range_check_ptr, bitwise_ptr: BitwiseBuiltin*, keccak_ptr: KeccakBuiltin*}(
+    ) -> Hash32 {
+    tempvar buffer: Bytes;
+    %{ memory[ap - 1] = gen_arg(program_input["buffer"]) %}
+    let hash = keccak256(buffer);
+    return hash;
+}

cairo/tests/ethereum/crypto/test_hash.py

@@ -0,0 +1,12 @@
+import hypothesis.strategies as st
+from hypothesis import given
+
+from ethereum.crypto.hash import keccak256
+
+
+class TestHash:
+
+    class TestKeccak256:
+        @given(buffer=st.binary(min_size=0, max_size=1000))
+        def test_keccak256(self, cairo_run, buffer):
+            assert keccak256(buffer) == cairo_run("test_keccak256", buffer=buffer)