gsm0808: Add create functions for CIPHER MODE COMMAND

gsm0808.h/c lacks functionality to generate CIPHER MODE COMMAND messages. These
messages are required if the code is used in an MSC implementation.

This commit adds a gsm0808_create_cipher() function, that generates an A/AoiP
CIPHER MODE COMMAND message.

Change-Id: I8eb1c357860c3e740b0f5d17e1c256bc87920958

include/osmocom/gsm/gsm0808.h

@@ -35,6 +35,8 @@ struct msgb *gsm0808_create_reset(void);
 struct msgb *gsm0808_create_reset_ack(void);
 struct msgb *gsm0808_create_clear_command(uint8_t reason);
 struct msgb *gsm0808_create_clear_complete(void);
+struct msgb *gsm0808_create_cipher(const struct gsm0808_encrypt_info *ei,
+				   const uint8_t *cipher_response_mode);
 struct msgb *gsm0808_create_cipher_complete(struct msgb *layer3, uint8_t alg_id);
 struct msgb *gsm0808_create_cipher_reject(uint8_t cause);
 struct msgb *gsm0808_create_classmark_update(const uint8_t *cm2, uint8_t cm2_len,

src/gsm/gsm0808.c

@@ -131,6 +131,39 @@ struct msgb *gsm0808_create_clear_command(uint8_t reason)
 	return msg;
 }
 
+struct msgb *gsm0808_create_cipher(const struct gsm0808_encrypt_info *ei,
+				   const uint8_t *cipher_response_mode)
+{
+	/* See also: 3GPP TS 48.008 3.2.1.30 CIPHER MODE COMMAND */
+	struct msgb *msg;
+
+	/* Mandatory emelent! */
+	OSMO_ASSERT(ei);
+
+	msg =
+	    msgb_alloc_headroom(BSSMAP_MSG_SIZE, BSSMAP_MSG_HEADROOM,
+				"cipher-mode-command");
+	if (!msg)
+		return NULL;
+
+	/* Message Type 3.2.2.1 */
+	msgb_v_put(msg, BSS_MAP_MSG_CIPHER_MODE_CMD);
+
+	/* Encryption Information 3.2.2.10 */
+	gsm0808_enc_encrypt_info(msg, ei);
+
+	/* Cipher Response Mode 3.2.2.34 */
+	if (cipher_response_mode)
+		msgb_tv_put(msg, GSM0808_IE_CIPHER_RESPONSE_MODE,
+			    *cipher_response_mode);
+
+	/* pre-pend the header */
+	msg->l3h =
+	    msgb_tv_push(msg, BSSAP_MSG_BSS_MANAGEMENT, msgb_length(msg));
+
+	return msg;
+}
+
 struct msgb *gsm0808_create_cipher_complete(struct msgb *layer3, uint8_t alg_id)
 {
 	struct msgb *msg = msgb_alloc_headroom(BSSMAP_MSG_SIZE, BSSMAP_MSG_HEADROOM,

src/gsm/libosmogsm.map

@@ -128,6 +128,7 @@ gsm0808_create_assignment_completed;
 gsm0808_create_ass_compl;
 gsm0808_create_assignment_failure;
 gsm0808_create_ass_fail;
+gsm0808_create_cipher;
 gsm0808_create_cipher_complete;
 gsm0808_create_cipher_reject;
 gsm0808_create_classmark_update;

tests/gsm0808/gsm0808_test.c

@@ -144,6 +144,46 @@ static void test_create_clear_complete()
 	msgb_free(msg);
 }
 
+static void test_create_cipher()
+{
+	static const uint8_t res[] =
+	    { 0x00, 0x0c, 0x53, 0x0a, 0x09, 0x03, 0xaa,
+	      0xbb, 0xcc, 0xdd, 0xee, 0xff, 0x23, 0x42 };
+	static const uint8_t res2[] =
+	    { 0x00, 0x0e, 0x53, 0x0a, 0x09, 0x03, 0xaa,
+	      0xbb, 0xcc, 0xdd, 0xee, 0xff, 0x23, 0x42,
+	      GSM0808_IE_CIPHER_RESPONSE_MODE, 0x01 };
+	struct msgb *msg;
+	struct gsm0808_encrypt_info ei;
+	uint8_t include_imeisv;
+
+	memset(&ei, 0, sizeof(ei));
+	ei.perm_algo[0] = GSM0808_ALG_ID_A5_0;
+	ei.perm_algo[1] = GSM0808_ALG_ID_A5_1;
+	ei.perm_algo_len = 2;
+	ei.key[0] = 0xaa;
+	ei.key[1] = 0xbb;
+	ei.key[2] = 0xcc;
+	ei.key[3] = 0xdd;
+	ei.key[4] = 0xee;
+	ei.key[5] = 0xff;
+	ei.key[6] = 0x23;
+	ei.key[7] = 0x42;
+	ei.key_len = 8;
+	include_imeisv = 1;
+
+	printf("Testing creating Chipher Mode Command\n");
+	msg = gsm0808_create_cipher(&ei, NULL);
+	OSMO_ASSERT(msg);
+	VERIFY(msg, res, ARRAY_SIZE(res));
+	msgb_free(msg);
+
+	msg = gsm0808_create_cipher(&ei, &include_imeisv);
+	OSMO_ASSERT(msg);
+	VERIFY(msg, res2, ARRAY_SIZE(res2));
+	msgb_free(msg);
+}
+
 static void test_create_cipher_complete()
 {
 	static const uint8_t res1[] = {
@@ -700,6 +740,7 @@ int main(int argc, char **argv)
 	test_create_reset();
 	test_create_clear_command();
 	test_create_clear_complete();
+	test_create_cipher();
 	test_create_cipher_complete();
 	test_create_cipher_reject();
 	test_create_cm_u();

tests/gsm0808/gsm0808_test.ok

@@ -4,6 +4,7 @@ Testing creating Layer3 (AoIP)
 Testing creating Reset
 Testing creating Clear Command
 Testing creating Clear Complete
+Testing creating Chipher Mode Command
 Testing creating Cipher Complete
 Testing creating Cipher Reject
 Testing creating CM U