--- /n/sources/plan9/sys/include/libsec.h	Mon Jun 24 19:54:05 2024
+++ /sys/include/libsec.h	Tue Jun 23 00:00:00 2026
@@ -182,6 +182,7 @@ enum
 	MD5dlen=	16,	/* MD5 digest length */
 	AESdlen=	16,	/* TODO: see rfc */
 	Poly1305dlen=	16,	/* Poly1305 digest length */
+	Maxdlen=	64,
 
 	Hmacblksz	= 64,	/* in bytes; from rfc2104 */
 };
@@ -447,3 +448,11 @@ void	freecertchain(PEMChain *chain);
 /* password-based key derivation function 2 (rfc2898) */
 void pbkdf2_x(uchar *p, ulong plen, uchar *s, ulong slen, ulong rounds, uchar *d, ulong dlen,
 	DigestState* (*x)(uchar*, ulong, uchar*, ulong, uchar*, DigestState*), int xlen);
+
+/*
+ * HKDF
+ */
+void	hkdfExtract(uchar*, DigestState*(*)(uchar*, ulong, uchar*, DigestState*), int, uchar*, int, uchar*, int);
+int	hkdfExpand(uchar*, DigestState*(*)(uchar*, ulong, uchar*, DigestState*), int, uchar*, int, uchar*, int, int);
+int	hkdfKey(uchar*, DigestState*(*x)(uchar*, ulong, uchar*, DigestState*), int xlen, uchar*, int, uchar*, int, uchar*, int, int);
+
--- /n/sources/plan9/sys/include/ape/libsec.h	Thu Jan 31 10:50:06 2013
+++ /sys/include/ape/libsec.h	Tue Jun 23 00:00:00 2026
@@ -150,6 +150,7 @@ enum
 	MD4dlen=	16,	/* MD4 digest length */
 	MD5dlen=	16,	/* MD5 digest length */
 	AESdlen=	16,	/* TODO: see rfc */
+	Maxdlen=	64,
 
 	Hmacblksz	= 64,	/* in bytes; from rfc2104 */
 };
@@ -407,4 +408,11 @@ int	okThumbprint(uchar *sha1, Thumbprint *ok);
 uchar	*readcert(char *filename, int *pcertlen);
 PEMChain*readcertchain(char *filename);
 
+/*
+ * HKDF
+ */
+void	hkdfExtract(uchar*, DigestState*(*)(uchar*, ulong, uchar*, DigestState*), int, uchar*, int, uchar*, int);
+int	hkdfExpand(uchar*, DigestState*(*)(uchar*, ulong, uchar*, DigestState*), int, uchar*, int, uchar*, int, int);
+int	hkdfKey(uchar*, DigestState*(*x)(uchar*, ulong, uchar*, DigestState*), int xlen, uchar*, int, uchar*, int, uchar*, int, int);
+
 #endif
--- /dev/null	Tue Jun 23 12:32:15 2026
+++ /sys/src/libsec/port/hkdf.c	Tue Jun 23 00:00:00 2026
@@ -0,0 +1,105 @@
+// Derived from Go's src/crypto/hkdf/hkdf.go and
+// src/crypto/internal/fips140/hkdf/hkdf.go, which carry this notice:
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package hkdf implements the HMAC-based Extract-and-Expand Key Derivation
+// Function (HKDF) as defined in RFC 5869.
+//
+// HKDF is a cryptographic key derivation function (KDF) with the goal of
+// expanding limited input keying material into one or more cryptographically
+// strong secret keys.
+
+#include <u.h>
+#include <libc.h>
+#include <libsec.h>
+
+// hkdfExtract generates a pseudorandom key for use with hkdfExpand from an input
+// secret and an optional independent salt.
+//
+// Only use this function if you need to reuse the extracted key with multiple
+// Expand invocations and different context values. Most common scenarios,
+// including the generation of multiple keys, should use hkdfKey instead.
+void
+hkdfExtract(uchar *out, DigestState*(*x)(uchar*, ulong, uchar*, DigestState*), int xlen,
+uchar *secret, int nsecret, uchar *salt, int nsalt)
+{
+	uchar *s, zerosalt[Maxdlen] = { 0 };
+
+	assert(xlen <= Maxdlen);
+
+	s = salt;
+	if(s == nil) {
+		s = zerosalt;
+		nsalt = xlen;
+	}
+
+	hmac_x(secret, nsecret, s, nsalt, out, nil, x, xlen);
+}
+
+#define MIN(a, b)     ((a) < (b)? (a): (b))
+
+// hkdfExpand derives a key from the given hash, key, and optional context info,
+// returning a byte array in out of length keylen that can be used as cryptographic key.
+// The extraction step is skipped.
+//
+// The key should have been generated by hkdfExtract, or be a uniformly
+// random or pseudorandom cryptographically strong key. See RFC 5869, Section
+// 3.3. Most common scenarios will want to use hkdfKey instead.
+int
+hkdfExpand(uchar *out, DigestState*(*x)(uchar*, ulong, uchar*, DigestState*), int xlen,
+uchar *prk, int nprk, uchar *info, int ninfo, int keylen)
+{
+	u8int counter = 0;
+	uchar buf[Maxdlen] = { 0 };
+	int olen = 0, blen = 0, remain;
+	DigestState *s;
+
+	assert(xlen <= Maxdlen);
+
+	if(keylen > xlen * 255) {
+		werrstr("hkdf: requested key length too large");
+		return -1;
+	}
+
+	if(info == nil)
+		ninfo = 0;
+
+	while(olen < keylen) {
+		counter++;
+		assert(counter != 0);
+		s = hmac_x(buf, blen, prk, nprk, nil, nil, x, xlen);
+		hmac_x(info, ninfo, prk, nprk, nil, s, x, xlen);
+		hmac_x(&counter, 1, prk, nprk, buf, s, x, xlen);
+		blen = xlen;
+		remain  = keylen - olen;
+		remain = MIN(remain, blen);
+		memmove(out + olen, buf, remain);
+		olen += remain;
+	}
+
+	return 1;
+}
+
+// hkdfKey derives a key from the given hash, secret, salt and context info,
+// returning a byte array in out of length keylen that can be used as cryptographic key.
+// Salt and info can be nil.
+int
+hkdfKey(uchar *out, DigestState*(*x)(uchar*, ulong, uchar*, DigestState*),int xlen,
+uchar* secret, int nsecret, uchar* salt, int nsalt, uchar *info, int ninfo, int keylen)
+{
+	uchar prk[Maxdlen];
+
+	assert(xlen <= Maxdlen);
+
+	if(keylen > xlen * 255) {
+		werrstr("hkdf: requested key length too large");
+		return -1;
+	}
+
+	hkdfExtract(prk, x, xlen, secret, nsecret, salt, nsalt);
+	hkdfExpand(out, x, xlen, prk, xlen, info, ninfo, keylen);
+
+	return 1;
+}
--- /dev/null	Tue Jun 23 12:32:15 2026
+++ /sys/src/libsec/port/hkdftest.c	Tue Jun 23 00:00:00 2026
@@ -0,0 +1,410 @@
+// Derived from Go's src/cmd/go/src/crypto/hkdf/hkdf_test.go, which carries this notice:
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include <u.h>
+#include <libc.h>
+#include "libsec.h"
+
+typedef struct hkdfTest hkdfTest;
+struct hkdfTest {
+	DigestState*(*x)(uchar*, ulong, uchar*, DigestState*);
+	int xlen;
+	uchar master[128];
+	int nmaster;
+	uchar  salt[128];
+	int nsalt;
+	uchar  prk[128];
+	int nprk;
+	uchar  info[128];
+	int ninfo;
+	uchar  out[128];
+	int nout;
+};
+
+hkdfTest hkdfTests[] = {
+	// Tests from RFC 5869
+	{
+		sha2_256,
+		SHA2_256dlen,
+		{
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+		},
+		22,
+		{
+			0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+			0x08, 0x09, 0x0a, 0x0b, 0x0c,
+		},
+		13,
+		{
+			0x07, 0x77, 0x09, 0x36, 0x2c, 0x2e, 0x32, 0xdf,
+			0x0d, 0xdc, 0x3f, 0x0d, 0xc4, 0x7b, 0xba, 0x63,
+			0x90, 0xb6, 0xc7, 0x3b, 0xb5, 0x0f, 0x9c, 0x31,
+			0x22, 0xec, 0x84, 0x4a, 0xd7, 0xc2, 0xb3, 0xe5,
+		},
+		32,
+		{
+			0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
+			0xf8, 0xf9,
+		},
+		10,
+		{
+			0x3c, 0xb2, 0x5f, 0x25, 0xfa, 0xac, 0xd5, 0x7a,
+			0x90, 0x43, 0x4f, 0x64, 0xd0, 0x36, 0x2f, 0x2a,
+			0x2d, 0x2d, 0x0a, 0x90, 0xcf, 0x1a, 0x5a, 0x4c,
+			0x5d, 0xb0, 0x2d, 0x56, 0xec, 0xc4, 0xc5, 0xbf,
+			0x34, 0x00, 0x72, 0x08, 0xd5, 0xb8, 0x87, 0x18,
+			0x58, 0x65,
+		},
+		42,
+	},
+	{
+		sha2_256,
+		SHA2_256dlen,
+		{
+			0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+			0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
+			0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
+			0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
+			0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
+			0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
+			0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
+			0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
+			0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47,
+			0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
+		},
+		80,
+		{
+			0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,
+			0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
+			0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77,
+			0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f,
+			0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
+			0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
+			0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,
+			0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f,
+			0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
+			0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf,
+		},
+		80,
+		{
+			0x06, 0xa6, 0xb8, 0x8c, 0x58, 0x53, 0x36, 0x1a,
+			0x06, 0x10, 0x4c, 0x9c, 0xeb, 0x35, 0xb4, 0x5c,
+			0xef, 0x76, 0x00, 0x14, 0x90, 0x46, 0x71, 0x01,
+			0x4a, 0x19, 0x3f, 0x40, 0xc1, 0x5f, 0xc2, 0x44,
+		},
+		32,
+		{
+			0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7,
+			0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf,
+			0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
+			0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf,
+			0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7,
+			0xd8, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf,
+			0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
+			0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
+			0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
+			0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
+		},
+		80,
+		{
+			0xb1, 0x1e, 0x39, 0x8d, 0xc8, 0x03, 0x27, 0xa1,
+			0xc8, 0xe7, 0xf7, 0x8c, 0x59, 0x6a, 0x49, 0x34,
+			0x4f, 0x01, 0x2e, 0xda, 0x2d, 0x4e, 0xfa, 0xd8,
+			0xa0, 0x50, 0xcc, 0x4c, 0x19, 0xaf, 0xa9, 0x7c,
+			0x59, 0x04, 0x5a, 0x99, 0xca, 0xc7, 0x82, 0x72,
+			0x71, 0xcb, 0x41, 0xc6, 0x5e, 0x59, 0x0e, 0x09,
+			0xda, 0x32, 0x75, 0x60, 0x0c, 0x2f, 0x09, 0xb8,
+			0x36, 0x77, 0x93, 0xa9, 0xac, 0xa3, 0xdb, 0x71,
+			0xcc, 0x30, 0xc5, 0x81, 0x79, 0xec, 0x3e, 0x87,
+			0xc1, 0x4c, 0x01, 0xd5, 0xc1, 0xf3, 0x43, 0x4f,
+			0x1d, 0x87,
+		},
+		82,
+	},
+	{
+		sha2_256,
+		SHA2_256dlen,
+		{
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+		},
+		22,
+		{ 0 },
+		0,
+		{
+			0x19, 0xef, 0x24, 0xa3, 0x2c, 0x71, 0x7b, 0x16,
+			0x7f, 0x33, 0xa9, 0x1d, 0x6f, 0x64, 0x8b, 0xdf,
+			0x96, 0x59, 0x67, 0x76, 0xaf, 0xdb, 0x63, 0x77,
+			0xac, 0x43, 0x4c, 0x1c, 0x29, 0x3c, 0xcb, 0x04,
+		},
+		32,
+		{ 0 },
+		0,
+		{
+			0x8d, 0xa4, 0xe7, 0x75, 0xa5, 0x63, 0xc1, 0x8f,
+			0x71, 0x5f, 0x80, 0x2a, 0x06, 0x3c, 0x5a, 0x31,
+			0xb8, 0xa1, 0x1f, 0x5c, 0x5e, 0xe1, 0x87, 0x9e,
+			0xc3, 0x45, 0x4e, 0x5f, 0x3c, 0x73, 0x8d, 0x2d,
+			0x9d, 0x20, 0x13, 0x95, 0xfa, 0xa4, 0xb6, 0x1a,
+			0x96, 0xc8,
+		},
+		42,
+	},
+	{
+		sha2_256,
+		SHA2_256dlen,
+		{
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+		},
+		22,
+		// nil
+		{ 0 },
+		-1,	// replace values with a -1 length with nil
+		{
+			0x19, 0xef, 0x24, 0xa3, 0x2c, 0x71, 0x7b, 0x16,
+			0x7f, 0x33, 0xa9, 0x1d, 0x6f, 0x64, 0x8b, 0xdf,
+			0x96, 0x59, 0x67, 0x76, 0xaf, 0xdb, 0x63, 0x77,
+			0xac, 0x43, 0x4c, 0x1c, 0x29, 0x3c, 0xcb, 0x04,
+		},
+		32,
+		// nil
+		{ 0 },
+		-1, // replace values with a -1 length with nil
+		{
+			0x8d, 0xa4, 0xe7, 0x75, 0xa5, 0x63, 0xc1, 0x8f,
+			0x71, 0x5f, 0x80, 0x2a, 0x06, 0x3c, 0x5a, 0x31,
+			0xb8, 0xa1, 0x1f, 0x5c, 0x5e, 0xe1, 0x87, 0x9e,
+			0xc3, 0x45, 0x4e, 0x5f, 0x3c, 0x73, 0x8d, 0x2d,
+			0x9d, 0x20, 0x13, 0x95, 0xfa, 0xa4, 0xb6, 0x1a,
+			0x96, 0xc8,
+		},
+		42,
+	},
+	{
+		sha1,
+		SHA1dlen,
+		{
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b,
+		},
+		11,
+		{
+			0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+			0x08, 0x09, 0x0a, 0x0b, 0x0c,
+		},
+		13,
+		{
+			0x9b, 0x6c, 0x18, 0xc4, 0x32, 0xa7, 0xbf, 0x8f,
+			0x0e, 0x71, 0xc8, 0xeb, 0x88, 0xf4, 0xb3, 0x0b,
+			0xaa, 0x2b, 0xa2, 0x43,
+		},
+		20,
+		{
+			0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
+			0xf8, 0xf9,
+		},
+		10,
+		{
+			0x08, 0x5a, 0x01, 0xea, 0x1b, 0x10, 0xf3, 0x69,
+			0x33, 0x06, 0x8b, 0x56, 0xef, 0xa5, 0xad, 0x81,
+			0xa4, 0xf1, 0x4b, 0x82, 0x2f, 0x5b, 0x09, 0x15,
+			0x68, 0xa9, 0xcd, 0xd4, 0xf1, 0x55, 0xfd, 0xa2,
+			0xc2, 0x2e, 0x42, 0x24, 0x78, 0xd3, 0x05, 0xf3,
+			0xf8, 0x96,
+		},
+		42,
+	},
+	{
+		sha1,
+		SHA1dlen,
+		{
+			0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+			0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
+			0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
+			0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
+			0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
+			0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
+			0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
+			0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
+			0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47,
+			0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
+		},
+		80,
+		{
+			0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,
+			0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
+			0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77,
+			0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f,
+			0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
+			0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
+			0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,
+			0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f,
+			0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
+			0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf,
+		},
+		80,
+		{
+			0x8a, 0xda, 0xe0, 0x9a, 0x2a, 0x30, 0x70, 0x59,
+			0x47, 0x8d, 0x30, 0x9b, 0x26, 0xc4, 0x11, 0x5a,
+			0x22, 0x4c, 0xfa, 0xf6,
+		},
+		20,
+		{
+			0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7,
+			0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf,
+			0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
+			0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf,
+			0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7,
+			0xd8, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf,
+			0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
+			0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
+			0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
+			0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
+		},
+		80,
+		{
+			0x0b, 0xd7, 0x70, 0xa7, 0x4d, 0x11, 0x60, 0xf7,
+			0xc9, 0xf1, 0x2c, 0xd5, 0x91, 0x2a, 0x06, 0xeb,
+			0xff, 0x6a, 0xdc, 0xae, 0x89, 0x9d, 0x92, 0x19,
+			0x1f, 0xe4, 0x30, 0x56, 0x73, 0xba, 0x2f, 0xfe,
+			0x8f, 0xa3, 0xf1, 0xa4, 0xe5, 0xad, 0x79, 0xf3,
+			0xf3, 0x34, 0xb3, 0xb2, 0x02, 0xb2, 0x17, 0x3c,
+			0x48, 0x6e, 0xa3, 0x7c, 0xe3, 0xd3, 0x97, 0xed,
+			0x03, 0x4c, 0x7f, 0x9d, 0xfe, 0xb1, 0x5c, 0x5e,
+			0x92, 0x73, 0x36, 0xd0, 0x44, 0x1f, 0x4c, 0x43,
+			0x00, 0xe2, 0xcf, 0xf0, 0xd0, 0x90, 0x0b, 0x52,
+			0xd3, 0xb4,
+		},
+		82,
+	},
+	{
+		sha1,
+		SHA1dlen,
+		{
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+			0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
+		},
+		22,
+		{ 0 },
+		0,
+		{
+			0xda, 0x8c, 0x8a, 0x73, 0xc7, 0xfa, 0x77, 0x28,
+			0x8e, 0xc6, 0xf5, 0xe7, 0xc2, 0x97, 0x78, 0x6a,
+			0xa0, 0xd3, 0x2d, 0x01,
+		},
+		20,
+		{ 0 },
+		0,
+		{
+			0x0a, 0xc1, 0xaf, 0x70, 0x02, 0xb3, 0xd7, 0x61,
+			0xd1, 0xe5, 0x52, 0x98, 0xda, 0x9d, 0x05, 0x06,
+			0xb9, 0xae, 0x52, 0x05, 0x72, 0x20, 0xa3, 0x06,
+			0xe0, 0x7b, 0x6b, 0x87, 0xe8, 0xdf, 0x21, 0xd0,
+			0xea, 0x00, 0x03, 0x3d, 0xe0, 0x39, 0x84, 0xd3,
+			0x49, 0x18,
+		},
+		42,
+	},
+	{
+		sha1,
+		SHA1dlen,
+		{
+			0x0c, 0x0c, 0x0c, 0x0c, 0x0c, 0x0c, 0x0c, 0x0c,
+			0x0c, 0x0c, 0x0c, 0x0c, 0x0c, 0x0c, 0x0c, 0x0c,
+			0x0c, 0x0c, 0x0c, 0x0c, 0x0c, 0x0c,
+		},
+		22,
+		// nil
+		{ 0 },
+		-1, // replace values with a -1 length with nil
+		{
+			0x2a, 0xdc, 0xca, 0xda, 0x18, 0x77, 0x9e, 0x7c,
+			0x20, 0x77, 0xad, 0x2e, 0xb1, 0x9d, 0x3f, 0x3e,
+			0x73, 0x13, 0x85, 0xdd,
+		},
+		20,
+		// nil
+		{ 0 },
+		-1, // replace values with a -1 length with nil
+		{
+			0x2c, 0x91, 0x11, 0x72, 0x04, 0xd7, 0x45, 0xf3,
+			0x50, 0x0d, 0x63, 0x6a, 0x62, 0xf6, 0x4f, 0x0a,
+			0xb3, 0xba, 0xe5, 0x48, 0xaa, 0x53, 0xd4, 0x23,
+			0xb0, 0xd1, 0xf2, 0x7e, 0xbb, 0xa6, 0xf5, 0xe5,
+			0x67, 0x3a, 0x08, 0x1d, 0x70, 0xcc, 0xe7, 0xac,
+			0xfc, 0x48,
+		},
+		42,
+	},
+};
+
+void
+testHkdf(void)
+{
+	int i, j;
+	hkdfTest tt;
+	uchar *info, *salt, prk[128], key[128], expanded[128];
+
+	for(i = 0; i < nelem(hkdfTests); i++) {
+		 tt = hkdfTests[i];
+
+		// by convention, we send nil for values with a -1 length
+		info = tt.info;
+		if(tt.ninfo == -1) 
+			info = nil;
+		salt = tt.salt;
+		if(tt.nsalt == -1)
+			salt = nil;
+
+		hkdfExtract(prk, tt.x, tt.xlen, tt.master, tt.nmaster, salt, tt.nsalt);
+		if(memcmp(prk, tt.prk, tt.nprk) != 0)
+			print("%d: hkdfExtract: FAIL!\n", i);
+		for(j = 0; j< tt.nprk; j++)
+			print("%2.2ux", prk[j]);
+		print("\n");
+
+		hkdfKey(key, tt.x, tt.xlen, tt.master, tt.nmaster, salt, tt.nsalt, info, tt.ninfo, tt.nout);
+		if(memcmp(key, tt.out, tt.nout) != 0)
+			print("%d: hkdfKey: FAIL!\n", i);
+		for(j = 0; j < tt.nout; j++)
+			print("%2.2ux", key[j]);
+		print("\n");
+
+		hkdfExpand(expanded, tt.x, tt.xlen, prk, tt.nprk, info, tt.ninfo, tt.nout);
+		if(memcmp(expanded, tt.out, tt.nout) != 0)
+			print("%d: hkdfExpand: FAIL!\n", i);
+		for(j = 0; j < tt.nout; j++)
+			print("%2.2ux", expanded[j]);
+		print("\n");
+	}
+}
+
+void
+testHkdflimit(void)
+{
+	uchar master[] = { 0x00, 0x01,  0x02, 0x03};
+	char *info = "";
+	int limit = SHA1dlen * 255;
+	uchar key[SHA1dlen * 255 + 1];
+
+	if(hkdfKey(key, sha1, SHA1dlen, master, 4, nil, 0, (uchar*)info, 0, limit) != 1)
+		print("hkdfKey: limit: FAIL: key derivation\n");
+
+	if(hkdfKey(key, sha1, SHA1dlen, master, 4, nil, 0, (uchar*)info, 0, limit + 1) != -1)
+		print("hkdfKey: limit: FAIL: expected key derivation to fail, but it succeeded!\n");
+}
+
+void
+main(void)
+{
+	testHkdf();
+	testHkdflimit();
+}
--- /n/sources/plan9/sys/src/libsec/port/mkfile	Mon Jun 24 19:54:05 2024
+++ /sys/src/libsec/port/mkfile	Tue Jun 23 00:00:00 2026
@@ -19,6 +19,7 @@ CFILES = des.c desmodes.c desECB.c desCBC.c des3ECB.c des3CBC.c\
 	dsagen.c dsaalloc.c dsaprivtopub.c dsasign.c dsaverify.c \
 	tlshand.c thumb.c readcert.c \
 	pbkdf2.c\
+	hkdf.c\
 
 ALLOFILES=${CFILES:%.c=%.$O}
 
@@ -37,3 +38,6 @@ UPDATE=mkfile\
 
 $O.rsatest: rsatest.$O
 	$LD -o $target $prereq
+
+$O.hkdftest: hkdftest.$O
+	$LD -o $target $prereq
--- /dev/null	Tue Jun 23 12:32:15 2026
+++ /sys/man/2/hkdf	Tue Jun 23 00:00:00 2026
@@ -0,0 +1,100 @@
+.TH HKDF 2
+.SH NAME
+hkdfExpand, hkdfExtract, hkdfKey \- HMAC-based extract-and-expand key derivation function (HKDF)
+.SH SYNOPSIS
+.nr Wd \w'\fLvoid \fP'u
+.nr In \w'\fLvoid  \fP'u
+.ta \n(Wdu \w'\fLSHA1state* \fP'u +\n(Wdu +\n(Wdu +\n(Wdu +\n(Wdu
+.
+.de Ti
+.PP
+.in +\\n(Inu
+.ti -\\n(Inu
+.B
+.nh
+..
+.
+.ft L
+.nf
+#include <u.h>
+#include <libc.h>
+#include <libsec.h>
+#define DS DigestState	/* only to abbreviate SYNOPSIS */
+.fi
+.Ti
+int hkdfExpand(uchar *out, DS*(*x)(uchar*, ulong, uchar*, DS*), int xlen, uchar *prk, int nprk, uchar *info, int ninfo, int keylen)
+.Ti
+void hkdfExtract(uchar *out, DS*(*x)(uchar*, ulong, uchar*, DS*), int xlen, uchar *secret, int nsecret, uchar *salt, int nsalt)
+.Ti
+int hkdfKey(uchar *out, DS*(*x)(uchar*, ulong, uchar*, DS*), int xlen, uchar* secret, int nsecret, uchar* salt, int nsalt, uchar *info, int ninfo, int keylen)
+.SH DESCRIPTION
+.I hkdfExpand
+derives a key from the given
+.IR x
+.IR sechash(2)
+function, pseudo random key
+.IR prk ,
+and optional context
+.IR info ,
+returning a byte array in
+.IR out
+of length
+.IR keylen
+that can be used as cryptographic key.
+The extraction step is skipped.
+.PP
+The key should have been generated by
+.IR hkdfExtract ,
+or be a uniformly
+random or pseudorandom cryptographically strong key.
+See RFC 5869,
+Section 3.3.
+Most common scenarios will want to use
+.IR hkdfKey
+instead.
+.PP
+.I hkdfExtract
+generates a pseudorandom key in
+.IR out
+for use with
+.IR hkfExpand
+from an input
+.IR secret
+and an optional independent
+.IR salt .
+.PP
+Only use this function if you need to reuse the extracted key with multiple
+Expand invocations and different context values. Most common scenarios,
+including the generation of multiple keys, should use
+.IR hkdfKey
+instead.
+.PP
+.I hkdfKey
+derives a key from the given
+.IR x
+.IR sechash(2)
+function,
+.IR secret ,
+.IR salt
+and context
+.IR info ,
+returning a byte array in
+.IR out
+of length 
+.IR keylen
+that can be used as cryptographic key.
+.PP
+.IR Salt
+and
+.IR info
+may be
+.BR nil .
+.SH SOURCE
+.B /sys/src/libsec
+.SH SEE ALSO
+.IR sechash (2)
+.br
+RFC 5869
+.SH DIAGNOSTICS
+These functions set
+.IR errstr .