crypto: curve25519 - generic C library implementations

This contains two formally verified C implementations of the Curve25519
scalar multiplication function, one for 32-bit systems, and one for
64-bit systems whose compiler supports efficient 128-bit integer types.
Not only are these implementations formally verified, but they are also
the fastest available C implementations. They have been modified to be
friendly to kernel space and to be generally less horrendous looking,
but still an effort has been made to retain their formally verified
characteristic, and so the C might look slightly unidiomatic.

The 64-bit version comes from HACL*: https://github.com/project-everest/hacl-star
The 32-bit version comes from Fiat: https://github.com/mit-plv/fiat-crypto

Information: https://cr.yp.to/ecdh.html

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
[ardb: - move from lib/zinc to lib/crypto
       - replace .c #includes with Kconfig based object selection
       - drop simd handling and simplify support for per-arch versions ]
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 788 insertions, 0 deletions

diff --git a/lib/crypto/curve25519-hacl64.c b/lib/crypto/curve25519-hacl64.c
new file mode 100644
index 000000000000..771d82dc5f14
--- /dev/null
+++ b/lib/crypto/curve25519-hacl64.c
@@ -0,0 +1,788 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+/*
+ * Copyright (C) 2016-2017 INRIA and Microsoft Corporation.
+ * Copyright (C) 2018-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ *
+ * This is a machine-generated formally verified implementation of Curve25519
+ * ECDH from: <https://github.com/mitls/hacl-star>. Though originally machine
+ * generated, it has been tweaked to be suitable for use in the kernel. It is
+ * optimized for 64-bit machines that can efficiently work with 128-bit
+ * integer types.
+ */
+
+#include <asm/unaligned.h>
+#include <crypto/curve25519.h>
+#include <linux/string.h>
+
+typedef __uint128_t u128;
+
+static __always_inline u64 u64_eq_mask(u64 a, u64 b)
+{
+	u64 x = a ^ b;
+	u64 minus_x = ~x + (u64)1U;
+	u64 x_or_minus_x = x | minus_x;
+	u64 xnx = x_or_minus_x >> (u32)63U;
+	u64 c = xnx - (u64)1U;
+	return c;
+}
+
+static __always_inline u64 u64_gte_mask(u64 a, u64 b)
+{
+	u64 x = a;
+	u64 y = b;
+	u64 x_xor_y = x ^ y;
+	u64 x_sub_y = x - y;
+	u64 x_sub_y_xor_y = x_sub_y ^ y;
+	u64 q = x_xor_y | x_sub_y_xor_y;
+	u64 x_xor_q = x ^ q;
+	u64 x_xor_q_ = x_xor_q >> (u32)63U;
+	u64 c = x_xor_q_ - (u64)1U;
+	return c;
+}
+
+static __always_inline void modulo_carry_top(u64 *b)
+{
+	u64 b4 = b[4];
+	u64 b0 = b[0];
+	u64 b4_ = b4 & 0x7ffffffffffffLLU;
+	u64 b0_ = b0 + 19 * (b4 >> 51);
+	b[4] = b4_;
+	b[0] = b0_;
+}
+
+static __always_inline void fproduct_copy_from_wide_(u64 *output, u128 *input)
+{
+	{
+		u128 xi = input[0];
+		output[0] = ((u64)(xi));
+	}
+	{
+		u128 xi = input[1];
+		output[1] = ((u64)(xi));
+	}
+	{
+		u128 xi = input[2];
+		output[2] = ((u64)(xi));
+	}
+	{
+		u128 xi = input[3];
+		output[3] = ((u64)(xi));
+	}
+	{
+		u128 xi = input[4];
+		output[4] = ((u64)(xi));
+	}
+}
+
+static __always_inline void
+fproduct_sum_scalar_multiplication_(u128 *output, u64 *input, u64 s)
+{
+	output[0] += (u128)input[0] * s;
+	output[1] += (u128)input[1] * s;
+	output[2] += (u128)input[2] * s;
+	output[3] += (u128)input[3] * s;
+	output[4] += (u128)input[4] * s;
+}
+
+static __always_inline void fproduct_carry_wide_(u128 *tmp)
+{
+	{
+		u32 ctr = 0;
+		u128 tctr = tmp[ctr];
+		u128 tctrp1 = tmp[ctr + 1];
+		u64 r0 = ((u64)(tctr)) & 0x7ffffffffffffLLU;
+		u128 c = ((tctr) >> (51));
+		tmp[ctr] = ((u128)(r0));
+		tmp[ctr + 1] = ((tctrp1) + (c));
+	}
+	{
+		u32 ctr = 1;
+		u128 tctr = tmp[ctr];
+		u128 tctrp1 = tmp[ctr + 1];
+		u64 r0 = ((u64)(tctr)) & 0x7ffffffffffffLLU;
+		u128 c = ((tctr) >> (51));
+		tmp[ctr] = ((u128)(r0));
+		tmp[ctr + 1] = ((tctrp1) + (c));
+	}
+
+	{
+		u32 ctr = 2;
+		u128 tctr = tmp[ctr];
+		u128 tctrp1 = tmp[ctr + 1];
+		u64 r0 = ((u64)(tctr)) & 0x7ffffffffffffLLU;
+		u128 c = ((tctr) >> (51));
+		tmp[ctr] = ((u128)(r0));
+		tmp[ctr + 1] = ((tctrp1) + (c));
+	}
+	{
+		u32 ctr = 3;
+		u128 tctr = tmp[ctr];
+		u128 tctrp1 = tmp[ctr + 1];
+		u64 r0 = ((u64)(tctr)) & 0x7ffffffffffffLLU;
+		u128 c = ((tctr) >> (51));
+		tmp[ctr] = ((u128)(r0));
+		tmp[ctr + 1] = ((tctrp1) + (c));
+	}
+}
+
+static __always_inline void fmul_shift_reduce(u64 *output)
+{
+	u64 tmp = output[4];
+	u64 b0;
+	{
+		u32 ctr = 5 - 0 - 1;
+		u64 z = output[ctr - 1];
+		output[ctr] = z;
+	}
+	{
+		u32 ctr = 5 - 1 - 1;
+		u64 z = output[ctr - 1];
+		output[ctr] = z;
+	}
+	{
+		u32 ctr = 5 - 2 - 1;
+		u64 z = output[ctr - 1];
+		output[ctr] = z;
+	}
+	{
+		u32 ctr = 5 - 3 - 1;
+		u64 z = output[ctr - 1];
+		output[ctr] = z;
+	}
+	output[0] = tmp;
+	b0 = output[0];
+	output[0] = 19 * b0;
+}
+
+static __always_inline void fmul_mul_shift_reduce_(u128 *output, u64 *input,
+						   u64 *input21)
+{
+	u32 i;
+	u64 input2i;
+	{
+		u64 input2i = input21[0];
+		fproduct_sum_scalar_multiplication_(output, input, input2i);
+		fmul_shift_reduce(input);
+	}
+	{
+		u64 input2i = input21[1];
+		fproduct_sum_scalar_multiplication_(output, input, input2i);
+		fmul_shift_reduce(input);
+	}
+	{
+		u64 input2i = input21[2];
+		fproduct_sum_scalar_multiplication_(output, input, input2i);
+		fmul_shift_reduce(input);
+	}
+	{
+		u64 input2i = input21[3];
+		fproduct_sum_scalar_multiplication_(output, input, input2i);
+		fmul_shift_reduce(input);
+	}
+	i = 4;
+	input2i = input21[i];
+	fproduct_sum_scalar_multiplication_(output, input, input2i);
+}
+
+static __always_inline void fmul_fmul(u64 *output, u64 *input, u64 *input21)
+{
+	u64 tmp[5] = { input[0], input[1], input[2], input[3], input[4] };
+	{
+		u128 b4;
+		u128 b0;
+		u128 b4_;
+		u128 b0_;
+		u64 i0;
+		u64 i1;
+		u64 i0_;
+		u64 i1_;
+		u128 t[5] = { 0 };
+		fmul_mul_shift_reduce_(t, tmp, input21);
+		fproduct_carry_wide_(t);
+		b4 = t[4];
+		b0 = t[0];
+		b4_ = ((b4) & (((u128)(0x7ffffffffffffLLU))));
+		b0_ = ((b0) + (((u128)(19) * (((u64)(((b4) >> (51))))))));
+		t[4] = b4_;
+		t[0] = b0_;
+		fproduct_copy_from_wide_(output, t);
+		i0 = output[0];
+		i1 = output[1];
+		i0_ = i0 & 0x7ffffffffffffLLU;
+		i1_ = i1 + (i0 >> 51);
+		output[0] = i0_;
+		output[1] = i1_;
+	}
+}
+
+static __always_inline void fsquare_fsquare__(u128 *tmp, u64 *output)
+{
+	u64 r0 = output[0];
+	u64 r1 = output[1];
+	u64 r2 = output[2];
+	u64 r3 = output[3];
+	u64 r4 = output[4];
+	u64 d0 = r0 * 2;
+	u64 d1 = r1 * 2;
+	u64 d2 = r2 * 2 * 19;
+	u64 d419 = r4 * 19;
+	u64 d4 = d419 * 2;
+	u128 s0 = ((((((u128)(r0) * (r0))) + (((u128)(d4) * (r1))))) +
+		   (((u128)(d2) * (r3))));
+	u128 s1 = ((((((u128)(d0) * (r1))) + (((u128)(d4) * (r2))))) +
+		   (((u128)(r3 * 19) * (r3))));
+	u128 s2 = ((((((u128)(d0) * (r2))) + (((u128)(r1) * (r1))))) +
+		   (((u128)(d4) * (r3))));
+	u128 s3 = ((((((u128)(d0) * (r3))) + (((u128)(d1) * (r2))))) +
+		   (((u128)(r4) * (d419))));
+	u128 s4 = ((((((u128)(d0) * (r4))) + (((u128)(d1) * (r3))))) +
+		   (((u128)(r2) * (r2))));
+	tmp[0] = s0;
+	tmp[1] = s1;
+	tmp[2] = s2;
+	tmp[3] = s3;
+	tmp[4] = s4;
+}
+
+static __always_inline void fsquare_fsquare_(u128 *tmp, u64 *output)
+{
+	u128 b4;
+	u128 b0;
+	u128 b4_;
+	u128 b0_;
+	u64 i0;
+	u64 i1;
+	u64 i0_;
+	u64 i1_;
+	fsquare_fsquare__(tmp, output);
+	fproduct_carry_wide_(tmp);
+	b4 = tmp[4];
+	b0 = tmp[0];
+	b4_ = ((b4) & (((u128)(0x7ffffffffffffLLU))));
+	b0_ = ((b0) + (((u128)(19) * (((u64)(((b4) >> (51))))))));
+	tmp[4] = b4_;
+	tmp[0] = b0_;
+	fproduct_copy_from_wide_(output, tmp);
+	i0 = output[0];
+	i1 = output[1];
+	i0_ = i0 & 0x7ffffffffffffLLU;
+	i1_ = i1 + (i0 >> 51);
+	output[0] = i0_;
+	output[1] = i1_;
+}
+
+static __always_inline void fsquare_fsquare_times_(u64 *output, u128 *tmp,
+						   u32 count1)
+{
+	u32 i;
+	fsquare_fsquare_(tmp, output);
+	for (i = 1; i < count1; ++i)
+		fsquare_fsquare_(tmp, output);
+}
+
+static __always_inline void fsquare_fsquare_times(u64 *output, u64 *input,
+						  u32 count1)
+{
+	u128 t[5];
+	memcpy(output, input, 5 * sizeof(*input));
+	fsquare_fsquare_times_(output, t, count1);
+}
+
+static __always_inline void fsquare_fsquare_times_inplace(u64 *output,
+							  u32 count1)
+{
+	u128 t[5];
+	fsquare_fsquare_times_(output, t, count1);
+}
+
+static __always_inline void crecip_crecip(u64 *out, u64 *z)
+{
+	u64 buf[20] = { 0 };
+	u64 *a0 = buf;
+	u64 *t00 = buf + 5;
+	u64 *b0 = buf + 10;
+	u64 *t01;
+	u64 *b1;
+	u64 *c0;
+	u64 *a;
+	u64 *t0;
+	u64 *b;
+	u64 *c;
+	fsquare_fsquare_times(a0, z, 1);
+	fsquare_fsquare_times(t00, a0, 2);
+	fmul_fmul(b0, t00, z);
+	fmul_fmul(a0, b0, a0);
+	fsquare_fsquare_times(t00, a0, 1);
+	fmul_fmul(b0, t00, b0);
+	fsquare_fsquare_times(t00, b0, 5);
+	t01 = buf + 5;
+	b1 = buf + 10;
+	c0 = buf + 15;
+	fmul_fmul(b1, t01, b1);
+	fsquare_fsquare_times(t01, b1, 10);
+	fmul_fmul(c0, t01, b1);
+	fsquare_fsquare_times(t01, c0, 20);
+	fmul_fmul(t01, t01, c0);
+	fsquare_fsquare_times_inplace(t01, 10);
+	fmul_fmul(b1, t01, b1);
+	fsquare_fsquare_times(t01, b1, 50);
+	a = buf;
+	t0 = buf + 5;
+	b = buf + 10;
+	c = buf + 15;
+	fmul_fmul(c, t0, b);
+	fsquare_fsquare_times(t0, c, 100);
+	fmul_fmul(t0, t0, c);
+	fsquare_fsquare_times_inplace(t0, 50);
+	fmul_fmul(t0, t0, b);
+	fsquare_fsquare_times_inplace(t0, 5);
+	fmul_fmul(out, t0, a);
+}
+
+static __always_inline void fsum(u64 *a, u64 *b)
+{
+	a[0] += b[0];
+	a[1] += b[1];
+	a[2] += b[2];
+	a[3] += b[3];
+	a[4] += b[4];
+}
+
+static __always_inline void fdifference(u64 *a, u64 *b)
+{
+	u64 tmp[5] = { 0 };
+	u64 b0;
+	u64 b1;
+	u64 b2;
+	u64 b3;
+	u64 b4;
+	memcpy(tmp, b, 5 * sizeof(*b));
+	b0 = tmp[0];
+	b1 = tmp[1];
+	b2 = tmp[2];
+	b3 = tmp[3];
+	b4 = tmp[4];
+	tmp[0] = b0 + 0x3fffffffffff68LLU;
+	tmp[1] = b1 + 0x3ffffffffffff8LLU;
+	tmp[2] = b2 + 0x3ffffffffffff8LLU;
+	tmp[3] = b3 + 0x3ffffffffffff8LLU;
+	tmp[4] = b4 + 0x3ffffffffffff8LLU;
+	{
+		u64 xi = a[0];
+		u64 yi = tmp[0];
+		a[0] = yi - xi;
+	}
+	{
+		u64 xi = a[1];
+		u64 yi = tmp[1];
+		a[1] = yi - xi;
+	}
+	{
+		u64 xi = a[2];
+		u64 yi = tmp[2];
+		a[2] = yi - xi;
+	}
+	{
+		u64 xi = a[3];
+		u64 yi = tmp[3];
+		a[3] = yi - xi;
+	}
+	{
+		u64 xi = a[4];
+		u64 yi = tmp[4];
+		a[4] = yi - xi;
+	}
+}
+
+static __always_inline void fscalar(u64 *output, u64 *b, u64 s)
+{
+	u128 tmp[5];
+	u128 b4;
+	u128 b0;
+	u128 b4_;
+	u128 b0_;
+	{
+		u64 xi = b[0];
+		tmp[0] = ((u128)(xi) * (s));
+	}
+	{
+		u64 xi = b[1];
+		tmp[1] = ((u128)(xi) * (s));
+	}
+	{
+		u64 xi = b[2];
+		tmp[2] = ((u128)(xi) * (s));
+	}
+	{
+		u64 xi = b[3];
+		tmp[3] = ((u128)(xi) * (s));
+	}
+	{
+		u64 xi = b[4];
+		tmp[4] = ((u128)(xi) * (s));
+	}
+	fproduct_carry_wide_(tmp);
+	b4 = tmp[4];
+	b0 = tmp[0];
+	b4_ = ((b4) & (((u128)(0x7ffffffffffffLLU))));
+	b0_ = ((b0) + (((u128)(19) * (((u64)(((b4) >> (51))))))));
+	tmp[4] = b4_;
+	tmp[0] = b0_;
+	fproduct_copy_from_wide_(output, tmp);
+}
+
+static __always_inline void fmul(u64 *output, u64 *a, u64 *b)
+{
+	fmul_fmul(output, a, b);
+}
+
+static __always_inline void crecip(u64 *output, u64 *input)
+{
+	crecip_crecip(output, input);
+}
+
+static __always_inline void point_swap_conditional_step(u64 *a, u64 *b,
+							u64 swap1, u32 ctr)
+{
+	u32 i = ctr - 1;
+	u64 ai = a[i];
+	u64 bi = b[i];
+	u64 x = swap1 & (ai ^ bi);
+	u64 ai1 = ai ^ x;
+	u64 bi1 = bi ^ x;
+	a[i] = ai1;
+	b[i] = bi1;
+}
+
+static __always_inline void point_swap_conditional5(u64 *a, u64 *b, u64 swap1)
+{
+	point_swap_conditional_step(a, b, swap1, 5);
+	point_swap_conditional_step(a, b, swap1, 4);
+	point_swap_conditional_step(a, b, swap1, 3);
+	point_swap_conditional_step(a, b, swap1, 2);
+	point_swap_conditional_step(a, b, swap1, 1);
+}
+
+static __always_inline void point_swap_conditional(u64 *a, u64 *b, u64 iswap)
+{
+	u64 swap1 = 0 - iswap;
+	point_swap_conditional5(a, b, swap1);
+	point_swap_conditional5(a + 5, b + 5, swap1);
+}
+
+static __always_inline void point_copy(u64 *output, u64 *input)
+{
+	memcpy(output, input, 5 * sizeof(*input));
+	memcpy(output + 5, input + 5, 5 * sizeof(*input));
+}
+
+static __always_inline void addanddouble_fmonty(u64 *pp, u64 *ppq, u64 *p,
+						u64 *pq, u64 *qmqp)
+{
+	u64 *qx = qmqp;
+	u64 *x2 = pp;
+	u64 *z2 = pp + 5;
+	u64 *x3 = ppq;
+	u64 *z3 = ppq + 5;
+	u64 *x = p;
+	u64 *z = p + 5;
+	u64 *xprime = pq;
+	u64 *zprime = pq + 5;
+	u64 buf[40] = { 0 };
+	u64 *origx = buf;
+	u64 *origxprime0 = buf + 5;
+	u64 *xxprime0;
+	u64 *zzprime0;
+	u64 *origxprime;
+	xxprime0 = buf + 25;
+	zzprime0 = buf + 30;
+	memcpy(origx, x, 5 * sizeof(*x));
+	fsum(x, z);
+	fdifference(z, origx);
+	memcpy(origxprime0, xprime, 5 * sizeof(*xprime));
+	fsum(xprime, zprime);
+	fdifference(zprime, origxprime0);
+	fmul(xxprime0, xprime, z);
+	fmul(zzprime0, x, zprime);
+	origxprime = buf + 5;
+	{
+		u64 *xx0;
+		u64 *zz0;
+		u64 *xxprime;
+		u64 *zzprime;
+		u64 *zzzprime;
+		xx0 = buf + 15;
+		zz0 = buf + 20;
+		xxprime = buf + 25;
+		zzprime = buf + 30;
+		zzzprime = buf + 35;
+		memcpy(origxprime, xxprime, 5 * sizeof(*xxprime));
+		fsum(xxprime, zzprime);
+		fdifference(zzprime, origxprime);
+		fsquare_fsquare_times(x3, xxprime, 1);
+		fsquare_fsquare_times(zzzprime, zzprime, 1);
+		fmul(z3, zzzprime, qx);
+		fsquare_fsquare_times(xx0, x, 1);
+		fsquare_fsquare_times(zz0, z, 1);
+		{
+			u64 *zzz;
+			u64 *xx;
+			u64 *zz;
+			u64 scalar;
+			zzz = buf + 10;
+			xx = buf + 15;
+			zz = buf + 20;
+			fmul(x2, xx, zz);
+			fdifference(zz, xx);
+			scalar = 121665;
+			fscalar(zzz, zz, scalar);
+			fsum(zzz, xx);
+			fmul(z2, zzz, zz);
+		}
+	}
+}
+
+static __always_inline void
+ladder_smallloop_cmult_small_loop_step(u64 *nq, u64 *nqpq, u64 *nq2, u64 *nqpq2,
+				       u64 *q, u8 byt)
+{
+	u64 bit0 = (u64)(byt >> 7);
+	u64 bit;
+	point_swap_conditional(nq, nqpq, bit0);
+	addanddouble_fmonty(nq2, nqpq2, nq, nqpq, q);
+	bit = (u64)(byt >> 7);
+	point_swap_conditional(nq2, nqpq2, bit);
+}
+
+static __always_inline void
+ladder_smallloop_cmult_small_loop_double_step(u64 *nq, u64 *nqpq, u64 *nq2,
+					      u64 *nqpq2, u64 *q, u8 byt)
+{
+	u8 byt1;
+	ladder_smallloop_cmult_small_loop_step(nq, nqpq, nq2, nqpq2, q, byt);
+	byt1 = byt << 1;
+	ladder_smallloop_cmult_small_loop_step(nq2, nqpq2, nq, nqpq, q, byt1);
+}
+
+static __always_inline void
+ladder_smallloop_cmult_small_loop(u64 *nq, u64 *nqpq, u64 *nq2, u64 *nqpq2,
+				  u64 *q, u8 byt, u32 i)
+{
+	while (i--) {
+		ladder_smallloop_cmult_small_loop_double_step(nq, nqpq, nq2,
+							      nqpq2, q, byt);
+		byt <<= 2;
+	}
+}
+
+static __always_inline void ladder_bigloop_cmult_big_loop(u8 *n1, u64 *nq,
+							  u64 *nqpq, u64 *nq2,
+							  u64 *nqpq2, u64 *q,
+							  u32 i)
+{
+	while (i--) {
+		u8 byte = n1[i];
+		ladder_smallloop_cmult_small_loop(nq, nqpq, nq2, nqpq2, q,
+						  byte, 4);
+	}
+}
+
+static void ladder_cmult(u64 *result, u8 *n1, u64 *q)
+{
+	u64 point_buf[40] = { 0 };
+	u64 *nq = point_buf;
+	u64 *nqpq = point_buf + 10;
+	u64 *nq2 = point_buf + 20;
+	u64 *nqpq2 = point_buf + 30;
+	point_copy(nqpq, q);
+	nq[0] = 1;
+	ladder_bigloop_cmult_big_loop(n1, nq, nqpq, nq2, nqpq2, q, 32);
+	point_copy(result, nq);
+}
+
+static __always_inline void format_fexpand(u64 *output, const u8 *input)
+{
+	const u8 *x00 = input + 6;
+	const u8 *x01 = input + 12;
+	const u8 *x02 = input + 19;
+	const u8 *x0 = input + 24;
+	u64 i0, i1, i2, i3, i4, output0, output1, output2, output3, output4;
+	i0 = get_unaligned_le64(input);
+	i1 = get_unaligned_le64(x00);
+	i2 = get_unaligned_le64(x01);
+	i3 = get_unaligned_le64(x02);
+	i4 = get_unaligned_le64(x0);
+	output0 = i0 & 0x7ffffffffffffLLU;
+	output1 = i1 >> 3 & 0x7ffffffffffffLLU;
+	output2 = i2 >> 6 & 0x7ffffffffffffLLU;
+	output3 = i3 >> 1 & 0x7ffffffffffffLLU;
+	output4 = i4 >> 12 & 0x7ffffffffffffLLU;
+	output[0] = output0;
+	output[1] = output1;
+	output[2] = output2;
+	output[3] = output3;
+	output[4] = output4;
+}
+
+static __always_inline void format_fcontract_first_carry_pass(u64 *input)
+{
+	u64 t0 = input[0];
+	u64 t1 = input[1];
+	u64 t2 = input[2];
+	u64 t3 = input[3];
+	u64 t4 = input[4];
+	u64 t1_ = t1 + (t0 >> 51);
+	u64 t0_ = t0 & 0x7ffffffffffffLLU;
+	u64 t2_ = t2 + (t1_ >> 51);
+	u64 t1__ = t1_ & 0x7ffffffffffffLLU;
+	u64 t3_ = t3 + (t2_ >> 51);
+	u64 t2__ = t2_ & 0x7ffffffffffffLLU;
+	u64 t4_ = t4 + (t3_ >> 51);
+	u64 t3__ = t3_ & 0x7ffffffffffffLLU;
+	input[0] = t0_;
+	input[1] = t1__;
+	input[2] = t2__;
+	input[3] = t3__;
+	input[4] = t4_;
+}
+
+static __always_inline void format_fcontract_first_carry_full(u64 *input)
+{
+	format_fcontract_first_carry_pass(input);
+	modulo_carry_top(input);
+}
+
+static __always_inline void format_fcontract_second_carry_pass(u64 *input)
+{
+	u64 t0 = input[0];
+	u64 t1 = input[1];
+	u64 t2 = input[2];
+	u64 t3 = input[3];
+	u64 t4 = input[4];
+	u64 t1_ = t1 + (t0 >> 51);
+	u64 t0_ = t0 & 0x7ffffffffffffLLU;
+	u64 t2_ = t2 + (t1_ >> 51);
+	u64 t1__ = t1_ & 0x7ffffffffffffLLU;
+	u64 t3_ = t3 + (t2_ >> 51);
+	u64 t2__ = t2_ & 0x7ffffffffffffLLU;
+	u64 t4_ = t4 + (t3_ >> 51);
+	u64 t3__ = t3_ & 0x7ffffffffffffLLU;
+	input[0] = t0_;
+	input[1] = t1__;
+	input[2] = t2__;
+	input[3] = t3__;
+	input[4] = t4_;
+}
+
+static __always_inline void format_fcontract_second_carry_full(u64 *input)
+{
+	u64 i0;
+	u64 i1;
+	u64 i0_;
+	u64 i1_;
+	format_fcontract_second_carry_pass(input);
+	modulo_carry_top(input);
+	i0 = input[0];
+	i1 = input[1];
+	i0_ = i0 & 0x7ffffffffffffLLU;
+	i1_ = i1 + (i0 >> 51);
+	input[0] = i0_;
+	input[1] = i1_;
+}
+
+static __always_inline void format_fcontract_trim(u64 *input)
+{
+	u64 a0 = input[0];
+	u64 a1 = input[1];
+	u64 a2 = input[2];
+	u64 a3 = input[3];
+	u64 a4 = input[4];
+	u64 mask0 = u64_gte_mask(a0, 0x7ffffffffffedLLU);
+	u64 mask1 = u64_eq_mask(a1, 0x7ffffffffffffLLU);
+	u64 mask2 = u64_eq_mask(a2, 0x7ffffffffffffLLU);
+	u64 mask3 = u64_eq_mask(a3, 0x7ffffffffffffLLU);
+	u64 mask4 = u64_eq_mask(a4, 0x7ffffffffffffLLU);
+	u64 mask = (((mask0 & mask1) & mask2) & mask3) & mask4;
+	u64 a0_ = a0 - (0x7ffffffffffedLLU & mask);
+	u64 a1_ = a1 - (0x7ffffffffffffLLU & mask);
+	u64 a2_ = a2 - (0x7ffffffffffffLLU & mask);
+	u64 a3_ = a3 - (0x7ffffffffffffLLU & mask);
+	u64 a4_ = a4 - (0x7ffffffffffffLLU & mask);
+	input[0] = a0_;
+	input[1] = a1_;
+	input[2] = a2_;
+	input[3] = a3_;
+	input[4] = a4_;
+}
+
+static __always_inline void format_fcontract_store(u8 *output, u64 *input)
+{
+	u64 t0 = input[0];
+	u64 t1 = input[1];
+	u64 t2 = input[2];
+	u64 t3 = input[3];
+	u64 t4 = input[4];
+	u64 o0 = t1 << 51 | t0;
+	u64 o1 = t2 << 38 | t1 >> 13;
+	u64 o2 = t3 << 25 | t2 >> 26;
+	u64 o3 = t4 << 12 | t3 >> 39;
+	u8 *b0 = output;
+	u8 *b1 = output + 8;
+	u8 *b2 = output + 16;
+	u8 *b3 = output + 24;
+	put_unaligned_le64(o0, b0);
+	put_unaligned_le64(o1, b1);
+	put_unaligned_le64(o2, b2);
+	put_unaligned_le64(o3, b3);
+}
+
+static __always_inline void format_fcontract(u8 *output, u64 *input)
+{
+	format_fcontract_first_carry_full(input);
+	format_fcontract_second_carry_full(input);
+	format_fcontract_trim(input);
+	format_fcontract_store(output, input);
+}
+
+static __always_inline void format_scalar_of_point(u8 *scalar, u64 *point)
+{
+	u64 *x = point;
+	u64 *z = point + 5;
+	u64 buf[10] __aligned(32) = { 0 };
+	u64 *zmone = buf;
+	u64 *sc = buf + 5;
+	crecip(zmone, z);
+	fmul(sc, x, zmone);
+	format_fcontract(scalar, sc);
+}
+
+void curve25519_generic(u8 mypublic[CURVE25519_KEY_SIZE],
+			const u8 secret[CURVE25519_KEY_SIZE],
+			const u8 basepoint[CURVE25519_KEY_SIZE])
+{
+	u64 buf0[10] __aligned(32) = { 0 };
+	u64 *x0 = buf0;
+	u64 *z = buf0 + 5;
+	u64 *q;
+	format_fexpand(x0, basepoint);
+	z[0] = 1;
+	q = buf0;
+	{
+		u8 e[32] __aligned(32) = { 0 };
+		u8 *scalar;
+		memcpy(e, secret, 32);
+		curve25519_clamp_secret(e);
+		scalar = e;
+		{
+			u64 buf[15] = { 0 };
+			u64 *nq = buf;
+			u64 *x = nq;
+			x[0] = 1;
+			ladder_cmult(nq, scalar, q);
+			format_scalar_of_point(mypublic, nq);
+			memzero_explicit(buf, sizeof(buf));
+		}
+		memzero_explicit(e, sizeof(e));
+	}
+	memzero_explicit(buf0, sizeof(buf0));
+}