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sjqtentaclescursoragent
sjqtentacles
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Track 1: constant-time crypto FFI, memory zeroing, PSK resumption
Practical-security hardening for production readiness: - 1a: sml-crypto-ffi shim wrapping libsodium (X25519, ChaCha20-Poly1305) via MLton _import and Poly/ML Foreign. Cross-impl tests assert byte-identical output to the pure-SML oracles on RFC 8439 / RFC 7748. FFI path lives behind dedicated targets; default suite stays pure-SML. - 1b: SecureZero (sodium_memzero / pure fallback) and TlsClient.zeroize / TlsServer.zeroize / zeroizeConfig to overwrite traffic keys, secrets, and rsaPrivateKeyDer. Best-effort given SML string immutability (documented). - 1c: server-side PSK resumption accept path (pure SML): in-memory ticket store, binder verification over the truncated ClientHello, selected_identity echo, PSK key schedule, Cert/CertVerify omitted on resume. Binder mismatch -> fatal illegal_parameter. Both compilers green: 306 passed, 0 failed (was 280). Co-authored-by: Cursor <cursoragent@cursor.com>
1 parent d86bf37 commit 79c471b

20 files changed

Lines changed: 1457 additions & 34 deletions

‎Makefile‎

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@@ -1,12 +1,31 @@
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# sml-tls build
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MLTON ?= mlton
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CC ?= clang
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BIN := bin
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LIBDIR := lib/github.com/sjqtentacles/sml-tls
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FFIDIR := lib/github.com/sjqtentacles/sml-crypto-ffi
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TEST_MLB := test/sources.mlb
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SRCS := $(wildcard $(LIBDIR)/*.sml $(LIBDIR)/*.sig) \
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$(wildcard test/*.sml) $(TEST_MLB) $(LIBDIR)/sources.mlb
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.PHONY: all test poly test-poly all-tests clean
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# --- Track 1a/1b: libsodium constant-time crypto FFI shim ---
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# libsodium (Homebrew default on Apple Silicon). Override on other systems,
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# e.g. SODIUM_PREFIX=/usr or =/usr/local.
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SODIUM_PREFIX ?= /opt/homebrew
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SODIUM_INC := $(SODIUM_PREFIX)/include
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SODIUM_LIB := $(SODIUM_PREFIX)/lib
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# Shared-library extension: .dylib on macOS, .so elsewhere.
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ifeq ($(shell uname -s),Darwin)
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SHLIB_EXT := dylib
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else
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SHLIB_EXT := so
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endif
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FFI_SHIM := $(BIN)/libsmlcryptoffi.$(SHLIB_EXT)
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# MLton link flags to resolve the shim's _import symbols against the dylib
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# (and libsodium itself).
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FFI_LINK := -link-opt "-L$(BIN) -L$(SODIUM_LIB) -lsmlcryptoffi -lsodium -Wl,-rpath,$(BIN) -Wl,-rpath,$(SODIUM_LIB)"
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.PHONY: all test poly test-poly all-tests ffi-shim test-ffi test-ffi-poly test-ffi-all clean
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all: $(BIN)/test-mlton
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@@ -26,6 +45,31 @@ test-poly: $(BIN)/test-poly
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all-tests: test test-poly
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# --- FFI shim (Track 1a/1b) ---------------------------------------------
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# Build the libsodium constant-time crypto shim into a shared library that
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# MLton links against and Poly/ML loads at runtime via Foreign.loadLibrary.
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ffi-shim: $(FFI_SHIM)
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$(FFI_SHIM): $(FFIDIR)/shim.c | $(BIN)
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$(CC) -O2 -fPIC -shared -I$(SODIUM_INC) $< \
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-L$(SODIUM_LIB) -lsodium -o $@
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# MLton FFI test: byte-identity (shim == pure-SML oracle) on RFC vectors.
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test-ffi: $(FFI_SHIM) $(SRCS) test/sources-ffi-mlton.mlb \
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$(wildcard $(FFIDIR)/*.sml $(FFIDIR)/*.sig) | $(BIN)
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$(MLTON) -default-ann 'allowFFI true' $(FFI_LINK) \
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-output $(BIN)/test-ffi-mlton test/sources-ffi-mlton.mlb
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$(BIN)/test-ffi-mlton
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# Poly/ML FFI test: same suite via Foreign.loadLibrary on the shim.
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test-ffi-poly: $(FFI_SHIM) $(SRCS) test/sources-ffi-poly.mlb tools/polybuild \
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$(wildcard $(FFIDIR)/*.sml $(FFIDIR)/*.sig) | $(BIN)
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SML_CRYPTO_FFI_LIB=$(FFI_SHIM) \
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sh tools/polybuild -o $(BIN)/test-ffi-poly test/sources-ffi-poly.mlb
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SML_CRYPTO_FFI_LIB=$(FFI_SHIM) $(BIN)/test-ffi-poly
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test-ffi-all: test-ffi test-ffi-poly
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$(BIN):
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mkdir -p $(BIN)
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‎lib/github.com/sjqtentacles/sml-crypto-ffi/crypto_ffi.sig‎

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(* crypto_ffi.sig
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Constant-time crypto via an FFI shim over libsodium (Track 1a/1b).
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This signature is implemented twice -- once with MLton's `_import`
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(crypto_ffi_mlton.sml) and once with Poly/ML's `Foreign` structure
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(crypto_ffi_poly.sml) -- so the same `CryptoFfi` structure is available
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on both compilers. Each build selects exactly one implementation file.
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The interface intentionally mirrors the SHAPE of the pure-SML modules it
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replaces so it can be used as a near drop-in:
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- `dh` / `base` match X25519.dh / X25519.base
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- `seal` / `open'` match Aead.seal / Aead.open' for
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ChaCha20-Poly1305 (record-form: ct||tag)
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- `memzero` best-effort secure wipe (Track 1b)
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All byte material is RAW byte strings (one char per byte, 0-255), the
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same convention as the rest of the sjqtentacles crypto family. *)
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signature CRYPTO_FFI =
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sig
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(* Raised on a length/contract violation or an underlying libsodium error
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(distinct from an AEAD authentication failure, which is `NONE`). *)
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exception CryptoFfi of string
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(* Idempotent libsodium initialisation. The implementations call this
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lazily on first use, but it is exposed for explicit warm-up/tests. *)
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val init : unit -> unit
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(* X25519 (RFC 7748). `scalar` and `point` are 32-byte little-endian
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strings; the result is the 32-byte shared u-coordinate. libsodium
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clamps the scalar internally, matching X25519.dh. *)
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val dh : string -> string -> string
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(* Public key: dh scalar 9. 32-byte little-endian result. *)
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val base : string -> string
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(* 32, for symmetry with X25519.keySize. *)
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val keySize : int
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structure ChaCha20Poly1305 :
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sig
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(* seal key nonce aad plaintext -> ciphertext || 16-byte tag.
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`key` is 32 bytes, `nonce` is 12 bytes. Raises CryptoFfi on a
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length violation. *)
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val seal : string -> string -> string -> string -> string
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(* open' key nonce aad (ciphertext||tag) -> SOME plaintext | NONE.
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NONE iff the tag does not verify or the input is too short. *)
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val open' : string -> string -> string -> string -> string option
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end
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(* Overwrite the bytes currently held by a Word8Array using libsodium's
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sodium_memzero, which the optimizer may not elide (Track 1b). *)
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val memzero : Word8Array.array -> unit
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end

‎lib/github.com/sjqtentacles/sml-crypto-ffi/crypto_ffi_mlton.sml‎

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(* crypto_ffi_mlton.sml
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MLton implementation of CRYPTO_FFI using `_import` to call the libsodium
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shim (lib/.../sml-crypto-ffi/shim.c). The shim object/library is linked
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into the executable by the Makefile via `-link-opt`.
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This file uses MLton-only `_import` syntax and is NOT loaded under
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Poly/ML (which uses crypto_ffi_poly.sml instead). *)
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structure CryptoFfi :> CRYPTO_FFI =
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struct
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exception CryptoFfi of string
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val keySize = 32
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(* --- libsodium shim imports (see shim.c) --- *)
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val cInit = _import "sml_sodium_init" public : unit -> int;
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val cX25519 = _import "sml_x25519" public :
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Word8Array.array * Word8Array.array * Word8Array.array -> int;
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val cX25519Base = _import "sml_x25519_base" public :
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Word8Array.array * Word8Array.array -> int;
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val cSeal = _import "sml_chacha20poly1305_seal" public :
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Word8Array.array * Word8Array.array * int
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* Word8Array.array * int * Word8Array.array * Word8Array.array -> int;
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val cOpen = _import "sml_chacha20poly1305_open" public :
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Word8Array.array * Word8Array.array * int
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* Word8Array.array * int * Word8Array.array * Word8Array.array -> int;
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val cMemzero = _import "sml_memzero" public :
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Word8Array.array * int -> unit;
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(* --- byte string <-> Word8Array marshalling --- *)
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fun toArr (s : string) : Word8Array.array =
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Word8Array.tabulate (String.size s,
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fn i => Byte.charToByte (String.sub (s, i)))
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fun fromArr (a : Word8Array.array) : string =
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CharVector.tabulate (Word8Array.length a,
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fn i => Byte.byteToChar (Word8Array.sub (a, i)))
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val initialised = ref false
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fun init () =
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if !initialised then ()
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else
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let val r = cInit () in
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if r < 0 then raise CryptoFfi "sodium_init failed"
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else initialised := true
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end
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fun checkLen (what, s, n) =
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if String.size s <> n then
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raise CryptoFfi (what ^ " must be " ^ Int.toString n ^ " bytes, got "
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^ Int.toString (String.size s))
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else ()
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fun dh scalar point =
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( init ()
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; checkLen ("scalar", scalar, 32)
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; checkLen ("point", point, 32)
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; let
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val out = Word8Array.array (32, 0w0)
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val _ = cX25519 (out, toArr scalar, toArr point)
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(* A zero result (small-order point) returns -1; the pure-SML
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oracle just returns the zero output, so we mirror that and
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return the (zeroed) output rather than raising. *)
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in fromArr out end )
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fun base scalar =
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( init ()
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; checkLen ("scalar", scalar, 32)
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; let
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val out = Word8Array.array (32, 0w0)
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val _ = cX25519Base (out, toArr scalar)
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in fromArr out end )
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structure ChaCha20Poly1305 =
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struct
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fun seal key nonce aad plaintext =
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( init ()
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; checkLen ("key", key, 32)
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; checkLen ("nonce", nonce, 12)
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; let
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val m = toArr plaintext
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val ad = toArr aad
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val out = Word8Array.array (String.size plaintext + 16, 0w0)
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val n = cSeal (out, m, String.size plaintext,
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ad, String.size aad, toArr nonce, toArr key)
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in
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if n < 0 then raise CryptoFfi "chacha20poly1305 seal failed"
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else fromArr out
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end )
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fun open' key nonce aad sealed =
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( init ()
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; checkLen ("key", key, 32)
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; checkLen ("nonce", nonce, 12)
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; if String.size sealed < 16 then NONE
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else
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let
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val c = toArr sealed
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val ad = toArr aad
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val out = Word8Array.array (String.size sealed - 16, 0w0)
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val n = cOpen (out, c, String.size sealed,
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ad, String.size aad, toArr nonce, toArr key)
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in
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if n < 0 then NONE else SOME (fromArr out)
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end )
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end
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fun memzero a =
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( init (); cMemzero (a, Word8Array.length a) )
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end

‎lib/github.com/sjqtentacles/sml-crypto-ffi/crypto_ffi_poly.sml‎

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(* crypto_ffi_poly.sml
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Poly/ML implementation of CRYPTO_FFI using the `Foreign` structure to
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call the libsodium shim (lib/.../sml-crypto-ffi/shim.c), compiled to a
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shared library that this module loads at runtime via
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`Foreign.loadLibrary`.
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This file uses Poly/ML-only `Foreign` and is NOT loaded under MLton
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(which uses crypto_ffi_mlton.sml instead).
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Poly/ML's `cArrayPointer cUint8` marshals an SML `int array` to/from a
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C `unsigned char *`, so byte material crosses the boundary as `int
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array` (values 0-255). *)
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structure CryptoFfi :> CRYPTO_FFI =
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struct
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exception CryptoFfi of string
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val keySize = 32
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(* Locate the shim shared library. The Makefile builds it next to the
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test binary as bin/libsmlcryptoffi.dylib; we also try a few common
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spots so tests run from the repo root work regardless of cwd. *)
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local
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open Foreign
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fun ext () =
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case OS.Process.getEnv "SML_CRYPTO_FFI_LIB" of
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SOME p => [p]
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| NONE => []
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val candidates =
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ext () @
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[ "bin/libsmlcryptoffi.dylib",
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"bin/libsmlcryptoffi.so",
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"./libsmlcryptoffi.dylib",
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"libsmlcryptoffi.dylib",
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"libsmlcryptoffi.so" ]
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fun tryLoad [] = raise CryptoFfi "could not load libsmlcryptoffi shim library"
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| tryLoad (p :: ps) =
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(loadLibrary p handle _ => tryLoad ps)
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val lib = tryLoad candidates
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val byteArr = cArrayPointer cUint8
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in
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val cInit = buildCall0 (getSymbol lib "sml_sodium_init", (), cInt)
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val cX25519 = buildCall3 (getSymbol lib "sml_x25519",
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(byteArr, byteArr, byteArr), cInt)
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val cX25519Base = buildCall2 (getSymbol lib "sml_x25519_base",
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(byteArr, byteArr), cInt)
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val cSeal = buildCall7 (getSymbol lib "sml_chacha20poly1305_seal",
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(byteArr, byteArr, cInt, byteArr, cInt, byteArr, byteArr), cInt)
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val cOpen = buildCall7 (getSymbol lib "sml_chacha20poly1305_open",
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(byteArr, byteArr, cInt, byteArr, cInt, byteArr, byteArr), cInt)
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val cMemzeroI = buildCall2 (getSymbol lib "sml_memzero",
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(byteArr, cInt), cVoid)
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end
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(* --- byte string <-> int array (0-255) marshalling --- *)
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fun toArr (s : string) : int array =
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Array.tabulate (String.size s, fn i => Char.ord (String.sub (s, i)))
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fun fromArr (a : int array) : string =
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CharVector.tabulate (Array.length a, fn i => Char.chr (Array.sub (a, i)))
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val initialised = ref false
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fun init () =
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if !initialised then ()
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else
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let val r = cInit () in
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if r < 0 then raise CryptoFfi "sodium_init failed"
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else initialised := true
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end
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fun checkLen (what, s, n) =
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if String.size s <> n then
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raise CryptoFfi (what ^ " must be " ^ Int.toString n ^ " bytes, got "
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^ Int.toString (String.size s))
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else ()
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fun dh scalar point =
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( init ()
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; checkLen ("scalar", scalar, 32)
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; checkLen ("point", point, 32)
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; let
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val out = Array.array (32, 0)
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val _ = cX25519 (out, toArr scalar, toArr point)
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in fromArr out end )
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fun base scalar =
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( init ()
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; checkLen ("scalar", scalar, 32)
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; let
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val out = Array.array (32, 0)
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val _ = cX25519Base (out, toArr scalar)
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in fromArr out end )
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structure ChaCha20Poly1305 =
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struct
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fun seal key nonce aad plaintext =
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( init ()
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; checkLen ("key", key, 32)
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; checkLen ("nonce", nonce, 12)
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; let
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val out = Array.array (String.size plaintext + 16, 0)
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val n = cSeal (out, toArr plaintext, String.size plaintext,
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toArr aad, String.size aad, toArr nonce, toArr key)
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in
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if n < 0 then raise CryptoFfi "chacha20poly1305 seal failed"
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else fromArr out
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end )
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fun open' key nonce aad sealed =
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( init ()
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; checkLen ("key", key, 32)
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; checkLen ("nonce", nonce, 12)
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; if String.size sealed < 16 then NONE
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else
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let
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val out = Array.array (String.size sealed - 16, 0)
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val n = cOpen (out, toArr sealed, String.size sealed,
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toArr aad, String.size aad, toArr nonce, toArr key)
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in
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if n < 0 then NONE else SOME (fromArr out)
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end )
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end
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(* Word8Array path: copy into an int array, zero via the shim, then copy
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the zeros back so the caller's array is wiped too. (sodium_memzero on
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the temporary guarantees the value-zeroing is not elided.) *)
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fun memzero a =
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let
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val () = init ()
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val n = Word8Array.length a
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val tmp = Array.array (n, 0)
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val () = cMemzeroI (tmp, n)
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in
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Word8Array.modify (fn _ => 0w0) a
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end
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end

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