Add extensible hash primitives: SHA1, SHA256, SHA512

Introduces a `crypto` feature (on by default) that wires the RustCrypto
sha1/sha2 crates into a small `HashAlgo` registry. `register_primitives`
iterates `crypto::ALGOS` and installs one Forth host word per algorithm,
each with the stack effect

    ( c-addr u -- c-addr2 u2 )

reading `u` bytes from `c-addr` and writing the digest into a shared
`HASH_SCRATCH` region in linear memory (carved out between the float
stack and the dictionary).

Adding a new hash is a one-line entry in `ALGOS`. `register_host_primitive`
is now `pub` so downstream crates can extend the VM with their own I/O
host words without forking WAFER — kelvar (a deterministic password
manager on WAFER) is the first consumer.

- 4 unit tests (lib-level sha1/256/512 + registry sanity)
- 5 integration tests (in-VM `SHA1`/`SHA256`/`SHA512` against RFC-3174,
  FIPS-180, and the first-round S/KEY seed used by `hel`)
- All 437 existing lib tests still pass; `wafer-web` still builds for
  `wasm32-unknown-unknown` with the feature enabled

crates/core/src/crypto.rs

@@ -0,0 +1,111 @@
+//! Cryptographic hash primitives for WAFER.
+//!
+//! Provides a small registry of hash algorithms ([`ALGOS`]) and a Forth
+//! word per algorithm. Each word has stack effect:
+//!
+//! ```text
+//! ( c-addr u -- c-addr2 u2 )
+//! ```
+//!
+//! It hashes the `u` bytes starting at `c-addr` and writes the digest into
+//! the [`crate::memory::HASH_SCRATCH_BASE`] region. The output buffer is
+//! shared and overwritten by every subsequent hash call — copy the bytes
+//! out before the next invocation if you need to keep them.
+//!
+//! The registry is designed to grow: add a new entry to [`ALGOS`] and the
+//! word is registered automatically by
+//! [`crate::outer::ForthVM::register_crypto_words`].
+
+use sha1::{Digest as Sha1Digest, Sha1};
+use sha2::{Sha256, Sha512};
+
+/// One hash algorithm registered as a Forth word.
+pub struct HashAlgo {
+    /// Forth word name (uppercase by convention).
+    pub name: &'static str,
+    /// Digest length in bytes.
+    pub digest_len: usize,
+    /// Hash function.
+    pub hash: fn(&[u8]) -> Vec<u8>,
+}
+
+fn sha1_hash(input: &[u8]) -> Vec<u8> {
+    let mut h = Sha1::new();
+    h.update(input);
+    h.finalize().to_vec()
+}
+
+fn sha256_hash(input: &[u8]) -> Vec<u8> {
+    let mut h = Sha256::new();
+    h.update(input);
+    h.finalize().to_vec()
+}
+
+fn sha512_hash(input: &[u8]) -> Vec<u8> {
+    let mut h = Sha512::new();
+    h.update(input);
+    h.finalize().to_vec()
+}
+
+/// All hash algorithms registered as Forth words.
+pub const ALGOS: &[HashAlgo] = &[
+    HashAlgo {
+        name: "SHA1",
+        digest_len: 20,
+        hash: sha1_hash,
+    },
+    HashAlgo {
+        name: "SHA256",
+        digest_len: 32,
+        hash: sha256_hash,
+    },
+    HashAlgo {
+        name: "SHA512",
+        digest_len: 64,
+        hash: sha512_hash,
+    },
+];
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn hex(bytes: &[u8]) -> String {
+        let mut s = String::with_capacity(bytes.len() * 2);
+        for b in bytes {
+            s.push_str(&format!("{b:02x}"));
+        }
+        s
+    }
+
+    #[test]
+    fn sha1_rfc3174_abc() {
+        assert_eq!(hex(&sha1_hash(b"abc")), "a9993e364706816aba3e25717850c26c9cd0d89d");
+    }
+
+    #[test]
+    fn sha256_fips180_abc() {
+        assert_eq!(
+            hex(&sha256_hash(b"abc")),
+            "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"
+        );
+    }
+
+    #[test]
+    fn sha512_fips180_abc() {
+        assert_eq!(
+            hex(&sha512_hash(b"abc")),
+            concat!(
+                "ddaf35a193617abacc417349ae20413112e6fa4e89a97ea20a9eeee64b55d39a",
+                "2192992a274fc1a836ba3c23a3feebbd454d4423643ce80e2a9ac94fa54ca49f"
+            )
+        );
+    }
+
+    #[test]
+    fn registry_lengths_match() {
+        assert_eq!(ALGOS[0].digest_len, sha1_hash(b"").len());
+        assert_eq!(ALGOS[1].digest_len, sha256_hash(b"").len());
+        assert_eq!(ALGOS[2].digest_len, sha512_hash(b"").len());
+    }
+}

crates/core/src/lib.rs

@@ -16,6 +16,8 @@
 
 pub mod codegen;
 pub mod config;
+#[cfg(feature = "crypto")]
+pub mod crypto;
 pub mod dictionary;
 pub mod error;
 pub mod ir;

crates/core/src/memory.rs

@@ -59,8 +59,14 @@ pub const FLOAT_STACK_BASE: u32 = RETURN_STACK_BASE + RETURN_STACK_SIZE; // 0x25
 /// Size of float stack region.
 pub const FLOAT_STACK_SIZE: u32 = 2048; // 256 doubles
 
+/// Hash scratch region — output buffer for `SHA1`/`SHA256`/`SHA512` and
+/// other hash host words. Sized for the largest supported digest (SHA512 = 64 B).
+pub const HASH_SCRATCH_BASE: u32 = FLOAT_STACK_BASE + FLOAT_STACK_SIZE; // 0x2D40
+/// Size of hash scratch region.
+pub const HASH_SCRATCH_SIZE: u32 = 128;
+
 /// Dictionary region start. Grows upward.
-pub const DICTIONARY_BASE: u32 = FLOAT_STACK_BASE + FLOAT_STACK_SIZE; // 0x2D40
+pub const DICTIONARY_BASE: u32 = HASH_SCRATCH_BASE + HASH_SCRATCH_SIZE; // 0x2DC0
 
 /// Initial top of data stack (grows down from here).
 pub const DATA_STACK_TOP: u32 = DATA_STACK_BASE + DATA_STACK_SIZE;
@@ -113,7 +119,8 @@ mod tests {
         const { assert!(DATA_STACK_BASE >= PAD_BASE + PAD_SIZE) };
         const { assert!(RETURN_STACK_BASE >= DATA_STACK_BASE + DATA_STACK_SIZE) };
         const { assert!(FLOAT_STACK_BASE >= RETURN_STACK_BASE + RETURN_STACK_SIZE) };
-        const { assert!(DICTIONARY_BASE >= FLOAT_STACK_BASE + FLOAT_STACK_SIZE) };
+        const { assert!(HASH_SCRATCH_BASE >= FLOAT_STACK_BASE + FLOAT_STACK_SIZE) };
+        const { assert!(DICTIONARY_BASE >= HASH_SCRATCH_BASE + HASH_SCRATCH_SIZE) };
     }
 
     #[test]

crates/core/src/outer.rs

@@ -20,6 +20,8 @@ use crate::codegen::{CodegenConfig, CompiledModule, compile_consolidated_module,
 use crate::config::WaferConfig;
 use crate::dictionary::{Dictionary, DictionaryState, WordId};
 use crate::ir::IrOp;
+#[cfg(feature = "crypto")]
+use crate::memory::HASH_SCRATCH_BASE;
 use crate::memory::{
     CELL_SIZE, DATA_STACK_TOP, FLOAT_SIZE, FLOAT_STACK_BASE, FLOAT_STACK_TOP, INPUT_BUFFER_BASE,
     INPUT_BUFFER_SIZE, RETURN_STACK_TOP, SYSVAR_BASE_VAR, SYSVAR_HERE, SYSVAR_LEAVE_FLAG,
@@ -383,6 +385,12 @@ impl<R: Runtime> ForthVM<R> {
         s
     }
 
+    /// Mutable access to the underlying runtime — useful for tests and for
+    /// host shims that need to read or write WAFER linear memory directly.
+    pub fn runtime_mut(&mut self) -> &mut R {
+        &mut self.rt
+    }
+
     /// Read the current data stack contents (top-first).
     pub fn data_stack(&mut self) -> Vec<i32> {
         let sp = self.rt.get_dsp();
@@ -2286,7 +2294,10 @@ impl<R: Runtime> ForthVM<R> {
     }
 
     /// Register a primitive whose implementation is a host function (not IR-compiled).
-    fn register_host_primitive(
+    ///
+    /// Public so downstream crates (like `kelvar-cli`) can extend the VM with
+    /// their own I/O host words without forking WAFER.
+    pub fn register_host_primitive(
         &mut self,
         name: &str,
         immediate: bool,
@@ -2592,6 +2603,10 @@ impl<R: Runtime> ForthVM<R> {
         // -- Floating-Point word set --
         self.register_float_words()?;
 
+        // -- Crypto: SHA1, SHA256, SHA512 (gated) --
+        #[cfg(feature = "crypto")]
+        self.register_crypto_words()?;
+
         // Batch-compile all deferred IR primitives into a single WASM module
         self.batch_mode = false;
         self.batch_compile_deferred()?;
@@ -2636,6 +2651,45 @@ impl<R: Runtime> ForthVM<R> {
         Ok(())
     }
 
+    // -----------------------------------------------------------------------
+    // Crypto: SHA1 / SHA256 / SHA512 (and any algos in `crypto::ALGOS`)
+    // -----------------------------------------------------------------------
+
+    /// Register one Forth word per entry in [`crate::crypto::ALGOS`].
+    ///
+    /// Each word has stack effect `( c-addr u -- c-addr2 u2 )`: it hashes
+    /// the `u` bytes at `c-addr` and writes the digest into the shared
+    /// scratch region at [`crate::memory::HASH_SCRATCH_BASE`]. The output
+    /// is overwritten by every subsequent hash call.
+    #[cfg(feature = "crypto")]
+    fn register_crypto_words(&mut self) -> anyhow::Result<()> {
+        for algo in crate::crypto::ALGOS {
+            let hash_fn = algo.hash;
+            let digest_len = algo.digest_len as i32;
+            let func: HostFn = Box::new(move |ctx: &mut dyn HostAccess| {
+                // Pop ( c-addr u )
+                let dsp = ctx.get_dsp();
+                let u = ctx.mem_read_i32(dsp) as u32;
+                let c_addr = ctx.mem_read_i32(dsp + CELL_SIZE) as u32;
+
+                // Read input bytes and hash.
+                let bytes = ctx.mem_read_slice(c_addr, u as usize);
+                let digest = hash_fn(&bytes);
+
+                // Write digest to scratch.
+                ctx.mem_write_slice(HASH_SCRATCH_BASE, &digest);
+
+                // Push ( scratch-addr digest-len ) — same dsp position, two
+                // cells overwritten in place.
+                ctx.mem_write_i32(dsp + CELL_SIZE, HASH_SCRATCH_BASE as i32);
+                ctx.mem_write_i32(dsp, digest_len);
+                Ok(())
+            });
+            self.register_host_primitive(algo.name, false, func)?;
+        }
+        Ok(())
+    }
+
     // -----------------------------------------------------------------------
     // Priority 1: Loop support host functions
     // -----------------------------------------------------------------------