SAE-PK: A tool for generating SAE-PK Modifier and password

sae_pk_gen can be used to generate Modifier (M) and password for SAE-PK
based on a previously generated EC private key, Sec value (2..5), and
SSID.

For example, these commands can be used to generate the private key and
the needed hostapd configuration parameter options:

make sae_pk_gen
openssl ecparam -genkey -outform DER -out saepk.der -name prime256v1
./sae_pk_gen saepk.der 3 "SAE-PK test"

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>

hostapd/Makefile

@@ -19,6 +19,9 @@ endif
 ifndef LIBS_n
 LIBS_n := $(LIBS)
 endif
+ifndef LIBS_s
+LIBS_s := $(LIBS)
+endif
 endif
 
 CFLAGS += $(EXTRA_CFLAGS)
@@ -122,6 +125,7 @@ LIBS += -lbfd -ldl -liberty -lz
 LIBS_c += -lbfd -ldl -liberty -lz
 LIBS_h += -lbfd -ldl -liberty -lz
 LIBS_n += -lbfd -ldl -liberty -lz
+LIBS_s += -lbfd -ldl -liberty -lz
 endif
 endif
 
@@ -704,6 +708,7 @@ LIBS += -lssl
 endif
 OBJS += ../src/crypto/crypto_openssl.o
 HOBJS += ../src/crypto/crypto_openssl.o
+SOBJS += ../src/crypto/crypto_openssl.o
 ifdef NEED_FIPS186_2_PRF
 OBJS += ../src/crypto/fips_prf_openssl.o
 endif
@@ -711,9 +716,11 @@ NEED_TLS_PRF_SHA256=y
 LIBS += -lcrypto
 LIBS_h += -lcrypto
 LIBS_n += -lcrypto
+LIBS_s += -lcrypto
 ifdef CONFIG_TLS_ADD_DL
 LIBS += -ldl
 LIBS_h += -ldl
+LIBS_s += -ldl
 endif
 ifndef CONFIG_TLS_DEFAULT_CIPHERS
 CONFIG_TLS_DEFAULT_CIPHERS = "DEFAULT:!EXP:!LOW"
@@ -1345,6 +1352,28 @@ ifeq ($(CONFIG_TLS), linux)
 HOBJS += ../src/crypto/crypto_linux.o
 endif
 
+SOBJS += sae_pk_gen.o
+SOBJS +=  ../src/utils/common.o
+SOBJS += ../src/utils/os_$(CONFIG_OS).o
+SOBJS += ../src/utils/base64.o
+SOBJS += ../src/utils/wpa_debug.o
+SOBJS += ../src/utils/wpabuf.o
+ifdef CONFIG_WPA_TRACE
+SOBJS += ../src/utils/trace.o
+endif
+SOBJS += ../src/common/ieee802_11_common.o
+SOBJS += ../src/common/sae.o
+SOBJS += ../src/common/sae_pk.o
+SOBJS += ../src/common/dragonfly.o
+SOBJS += $(AESOBJS)
+SOBJS += ../src/crypto/sha256-prf.o
+SOBJS += ../src/crypto/sha384-prf.o
+SOBJS += ../src/crypto/sha512-prf.o
+SOBJS += ../src/crypto/dh_groups.o
+SOBJS += ../src/crypto/sha256-kdf.o
+SOBJS += ../src/crypto/sha384-kdf.o
+SOBJS += ../src/crypto/sha512-kdf.o
+
 nt_password_hash: $(NOBJS)
 	$(Q)$(CC) $(LDFLAGS) -o nt_password_hash $(NOBJS) $(LIBS_n)
 	@$(E) "  LD " $@
@@ -1353,6 +1382,10 @@ hlr_auc_gw: $(HOBJS)
 	$(Q)$(CC) $(LDFLAGS) -o hlr_auc_gw $(HOBJS) $(LIBS_h)
 	@$(E) "  LD " $@
 
+sae_pk_gen: $(SOBJS)
+	$(Q)$(CC) $(LDFLAGS) -o sae_pk_gen $(SOBJS) $(LIBS_s)
+	@$(E) "  LD " $@
+
 lcov-html:
 	lcov -c -d .. > lcov.info
 	genhtml lcov.info --output-directory lcov-html
@@ -1360,6 +1393,7 @@ lcov-html:
 clean:
 	$(MAKE) -C ../src clean
 	rm -f core *~ *.o hostapd hostapd_cli nt_password_hash hlr_auc_gw
+	rm -f sae_pk_gen
 	rm -f *.d *.gcno *.gcda *.gcov
 	rm -f lcov.info
 	rm -rf lcov-html

hostapd/sae_pk_gen.c

@@ -0,0 +1,160 @@
+/*
+ * SAE-PK password/modifier generator
+ * Copyright (c) 2020, The Linux Foundation
+ *
+ * This software may be distributed under the terms of the BSD license.
+ * See README for more details.
+ */
+
+#include "utils/includes.h"
+
+#include "utils/common.h"
+#include "utils/base64.h"
+#include "crypto/crypto.h"
+#include "common/sae.h"
+
+
+int main(int argc, char *argv[])
+{
+	char *der = NULL;
+	size_t der_len;
+	struct crypto_ec_key *key = NULL;
+	struct wpabuf *pub = NULL;
+	u8 *data = NULL, *m;
+	size_t data_len;
+	char *b64 = NULL, *pw = NULL, *pos, *src;
+	int sec, j;
+	int ret = -1;
+	u8 hash[SAE_MAX_HASH_LEN], fingerprint[SAE_MAX_HASH_LEN];
+	int group;
+	size_t hash_len;
+	unsigned long long i, expected;
+	char m_hex[2 * SAE_PK_M_LEN + 1];
+
+	wpa_debug_level = MSG_INFO;
+	if (os_program_init() < 0)
+		goto fail;
+
+	if (argc != 4) {
+		fprintf(stderr,
+			"usage: sae_pk_gen <DER ECPrivateKey file> <Sec:2..5> <SSID>\n");
+		goto fail;
+	}
+
+	sec = atoi(argv[2]);
+	if (sec < 2 || sec > 5) {
+		fprintf(stderr, "Invalid Sec value (allowed range: 2..5)\n");
+		goto fail;
+	}
+	expected = 1;
+	for (j = 0; j < sec; j++)
+		expected *= 256;
+
+	der = os_readfile(argv[1], &der_len);
+	if (!der) {
+		fprintf(stderr, "Could not read %s: %s\n",
+			argv[1], strerror(errno));
+		goto fail;
+	}
+
+	key = crypto_ec_key_parse_priv((u8 *) der, der_len);
+	if (!key) {
+		fprintf(stderr, "Could not parse ECPrivateKey\n");
+		goto fail;
+	}
+
+	pub = crypto_ec_key_get_subject_public_key(key);
+	if (!pub) {
+		fprintf(stderr, "Failed to build SubjectPublicKey\n");
+		goto fail;
+	}
+
+	group = crypto_ec_key_group(key);
+	switch (group) {
+	case 19:
+		hash_len = 32;
+		break;
+	case 20:
+		hash_len = 48;
+		break;
+	case 21:
+		hash_len = 64;
+		break;
+	default:
+		fprintf(stderr, "Unsupported private key group\n");
+		goto fail;
+	}
+
+	data_len = os_strlen(argv[3]) + SAE_PK_M_LEN + wpabuf_len(pub);
+	data = os_malloc(data_len);
+	if (!data) {
+		fprintf(stderr, "No memory for data buffer\n");
+		goto fail;
+	}
+	os_memcpy(data, argv[3], os_strlen(argv[3]));
+	m = data + os_strlen(argv[3]);
+	if (os_get_random(m, SAE_PK_M_LEN) < 0) {
+		fprintf(stderr, "Could not generate random Modifier M\n");
+		goto fail;
+	}
+	os_memcpy(m + SAE_PK_M_LEN, wpabuf_head(pub), wpabuf_len(pub));
+
+	fprintf(stderr, "Searching for a suitable Modifier M value\n");
+	for (i = 0;; i++) {
+		if (sae_hash(hash_len, data, data_len, hash) < 0) {
+			fprintf(stderr, "Hash failed\n");
+			goto fail;
+		}
+		if (hash[0] == 0 && hash[1] == 0) {
+			if (sec == 2 || (hash[2] & 0xf0) == 0)
+				fprintf(stderr, "\r%3.2f%%",
+					100.0 * (double) i / (double) expected);
+			for (j = 2; j < sec; j++) {
+				if (hash[j])
+					break;
+			}
+			if (j == sec)
+				break;
+		}
+		inc_byte_array(m, SAE_PK_M_LEN);
+	}
+
+	fprintf(stderr, "\nFound a valid hash in %llu iterations\n", i);
+	wpa_hexdump(MSG_DEBUG, "Valid hash", hash, hash_len);
+	fingerprint[0] = (sec - 2) << 6 | hash[sec] >> 2;
+	for (i = 1; i < hash_len - sec; i++)
+		fingerprint[i] = hash[sec + i - 1] << 6 | hash[sec + i] >> 2;
+	wpa_hexdump(MSG_DEBUG, "Fingerprint part for password",
+		    fingerprint, hash_len - sec);
+
+	b64 = base64_encode(der, der_len, NULL);
+	pw = sae_pk_base32_encode(fingerprint, (hash_len - sec) * 8 - 2);
+	if (!b64 || !pw ||
+	    wpa_snprintf_hex(m_hex, sizeof(m_hex), m, SAE_PK_M_LEN) < 0)
+		goto fail;
+	src = pos = b64;
+	while (*src) {
+		if (*src != '\n')
+			*pos++ = *src;
+		src++;
+	}
+	*pos = '\0';
+
+	printf("# SAE-PK password/M/private key for Sec=%d.\n", sec);
+	printf("# The password can be truncated from right to improve\n");
+	printf("# usability at the cost of security.\n");
+	printf("sae_password=%s|pk=%s:%s\n", pw, m_hex, b64);
+
+	ret = 0;
+fail:
+	os_free(der);
+	wpabuf_free(pub);
+	crypto_ec_key_deinit(key);
+	os_free(data);
+	os_free(b64);
+	os_free(pw);
+
+	os_program_deinit();
+
+	return ret;
+}