diff --git a/lib/decoding/osmocom/gsm/a5.c b/lib/decoding/osmocom/gsm/a5.c
new file mode 100644
index 0000000..9f4ede1
--- /dev/null
+++ b/lib/decoding/osmocom/gsm/a5.c
@@ -0,0 +1,446 @@
+/*
+ * Copyright (C) 2011  Sylvain Munaut <tnt@246tNt.com>
+ *
+ * All Rights Reserved
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+/*! \addtogroup a5
+ *  @{
+ *  Osmocom GSM ciphering algorithm implementation
+ *
+ *  Full reimplementation of A5/1,2,3,4 (split and threadsafe).
+ *
+ *  The logic behind the algorithm is taken from "A pedagogical implementation
+ *  of the GSM A5/1 and A5/2 "voice privacy" encryption algorithms." by
+ *  Marc Briceno, Ian Goldberg, and David Wagner.
+ */
+
+#include <errno.h>
+#include <string.h>
+#include <stdbool.h>
+
+#include <osmocom/gsm/a5.h>
+#include <osmocom/gsm/kasumi.h>
+//#include <osmocom/crypt/auth.h>
+
+/* Somme OS (like Nuttx) don't have ENOTSUP */
+#ifndef ENOTSUP
+#define ENOTSUP EINVAL
+#endif
+
+/* ------------------------------------------------------------------------ */
+/* A5/3&4                                                                   */
+/* ------------------------------------------------------------------------ */
+
+/*! Generate a GSM A5/4 cipher stream
+ *  \param[in] key 16 byte array for the key (as received from the SIM)
+ *  \param[in] fn Frame number
+ *  \param[out] dl Pointer to array of ubits to return Downlink cipher stream
+ *  \param[out] ul Pointer to array of ubits to return Uplink cipher stream
+ *  \param[in] fn_correct true if fn is a real GSM frame number and thus requires internal conversion
+ *
+ * Either (or both) of dl/ul should be NULL if not needed.
+ *
+ * Implementation based on specifications from 3GPP TS 55.216, 3GPP TR 55.919 and ETSI TS 135 202
+ * with slight simplifications (CE hardcoded to 0).
+ */
+void
+_a5_4(const uint8_t *ck, uint32_t fn, ubit_t *dl, ubit_t *ul, bool fn_correct)
+{
+       uint8_t i, gamma[32], uplink[15];
+       uint32_t fn_count = (fn_correct) ? osmo_a5_fn_count(fn) : fn;
+
+       if (ul) {
+               _kasumi_kgcore(0xF, 0, fn_count, 0, ck, gamma, 228);
+               for(i = 0; i < 15; i++) uplink[i] = (gamma[i + 14] << 2) + (gamma[i + 15] >> 6);
+               osmo_pbit2ubit(ul, uplink, 114);
+       }
+       if (dl) {
+               _kasumi_kgcore(0xF, 0, fn_count, 0, ck, gamma, 114);
+               osmo_pbit2ubit(dl, gamma, 114);
+       }
+}
+
+/*! Generate a GSM A5/3 cipher stream
+ *  \param[in] key 8 byte array for the key (as received from the SIM)
+ *  \param[in] fn Frame number
+ *  \param[out] dl Pointer to array of ubits to return Downlink cipher stream
+ *  \param[out] ul Pointer to array of ubits to return Uplink cipher stream
+ *  \param[in] fn_correct true if fn is a real GSM frame number and thus requires internal conversion
+ *
+ * Either (or both) of dl/ul should be NULL if not needed.
+ *
+ * Implementation based on specifications from 3GPP TS 55.216, 3GPP TR 55.919 and ETSI TS 135 202
+ * with slight simplifications (CE hardcoded to 0).
+ */
+void
+_a5_3(const uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul, bool fn_correct)
+{
+       uint8_t ck[16];
+       osmo_c4(ck, key);
+       /* internal function require 128 bit key so we expand by concatenating supplied 64 bit key */
+       _a5_4(ck, fn, dl, ul, fn_correct);
+}
+
+/* ------------------------------------------------------------------------ */
+/* A5/1&2 common stuff                                                                     */
+/* ------------------------------------------------------------------------ */
+
+#define A5_R1_LEN	19
+#define A5_R2_LEN	22
+#define A5_R3_LEN	23
+#define A5_R4_LEN	17	/* A5/2 only */
+
+#define A5_R1_MASK	((1<<A5_R1_LEN)-1)
+#define A5_R2_MASK	((1<<A5_R2_LEN)-1)
+#define A5_R3_MASK	((1<<A5_R3_LEN)-1)
+#define A5_R4_MASK	((1<<A5_R4_LEN)-1)
+
+#define A5_R1_TAPS	0x072000 /* x^19 + x^18 + x^17 + x^14 + 1 */
+#define A5_R2_TAPS	0x300000 /* x^22 + x^21 + 1 */
+#define A5_R3_TAPS	0x700080 /* x^23 + x^22 + x^21 + x^8 + 1 */
+#define A5_R4_TAPS	0x010800 /* x^17 + x^12 + 1 */
+
+/*! Computes parity of a 32-bit word
+ *  \param[in] x 32 bit word
+ *  \return Parity bit (xor of all bits) as 0 or 1
+ */
+static inline uint32_t
+_a5_12_parity(uint32_t x)
+{
+	x ^= x >> 16;
+	x ^= x >> 8;
+	x ^= x >> 4;
+	x &= 0xf;
+	return (0x6996 >> x) & 1;
+}
+
+/*! Compute majority bit from 3 taps
+ *  \param[in] v1 LFSR state ANDed with tap-bit
+ *  \param[in] v2 LFSR state ANDed with tap-bit
+ *  \param[in] v3 LFSR state ANDed with tap-bit
+ *  \return The majority bit (0 or 1)
+ */
+static inline uint32_t
+_a5_12_majority(uint32_t v1, uint32_t v2, uint32_t v3)
+{
+	return (!!v1 + !!v2 + !!v3) >= 2;
+}
+
+/*! Compute the next LFSR state
+ *  \param[in] r Current state
+ *  \param[in] mask LFSR mask
+ *  \param[in] taps LFSR taps
+ *  \return Next state
+ */
+static inline uint32_t
+_a5_12_clock(uint32_t r, uint32_t mask, uint32_t taps)
+{
+	return ((r << 1) & mask) | _a5_12_parity(r & taps);
+}
+
+
+/* ------------------------------------------------------------------------ */
+/* A5/1                                                                     */
+/* ------------------------------------------------------------------------ */
+
+#define A51_R1_CLKBIT	0x000100
+#define A51_R2_CLKBIT	0x000400
+#define A51_R3_CLKBIT	0x000400
+
+/*! GSM A5/1 Clocking function
+ *  \param[in] r Register state
+ *  \param[in] force Non-zero value disable conditional clocking
+ */
+static inline void
+_a5_1_clock(uint32_t r[], int force)
+{
+	int cb[3], maj;
+
+	cb[0] = !!(r[0] & A51_R1_CLKBIT);
+	cb[1] = !!(r[1] & A51_R2_CLKBIT);
+	cb[2] = !!(r[2] & A51_R3_CLKBIT);
+
+	maj = _a5_12_majority(cb[0], cb[1], cb[2]);
+
+	if (force || (maj == cb[0]))
+		r[0] = _a5_12_clock(r[0], A5_R1_MASK, A5_R1_TAPS);
+
+	if (force || (maj == cb[1]))
+		r[1] = _a5_12_clock(r[1], A5_R2_MASK, A5_R2_TAPS);
+
+	if (force || (maj == cb[2]))
+		r[2] = _a5_12_clock(r[2], A5_R3_MASK, A5_R3_TAPS);
+}
+
+/*! GSM A5/1 Output function
+ *  \param[in] r Register state
+ *  \return The A5/1 output function bit
+ */
+static inline uint8_t
+_a5_1_get_output(uint32_t r[])
+{
+	return	(r[0] >> (A5_R1_LEN-1)) ^
+		(r[1] >> (A5_R2_LEN-1)) ^
+		(r[2] >> (A5_R3_LEN-1));
+}
+
+/*! Generate a GSM A5/1 cipher stream
+ *  \param[in] key 8 byte array for the key (as received from the SIM)
+ *  \param[in] fn Frame number
+ *  \param[out] dl Pointer to array of ubits to return Downlink cipher stream
+ *  \param[out] ul Pointer to array of ubits to return Uplink cipher stream
+ *
+ * Either (or both) of dl/ul can be NULL if not needed.
+ */
+void
+_a5_1(const uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul)
+{
+	uint32_t r[3] = {0, 0, 0};
+	uint32_t fn_count;
+	uint32_t b;
+	int i;
+
+	/* Key load */
+	for (i=0; i<64; i++)
+	{
+		b = ( key[7 - (i>>3)] >> (i&7) ) & 1;
+
+		_a5_1_clock(r, 1);
+
+		r[0] ^= b;
+		r[1] ^= b;
+		r[2] ^= b;
+	}
+
+	/* Frame count load */
+	fn_count = osmo_a5_fn_count(fn);
+
+	for (i=0; i<22; i++)
+	{
+		b = (fn_count >> i) & 1;
+
+		_a5_1_clock(r, 1);
+
+		r[0] ^= b;
+		r[1] ^= b;
+		r[2] ^= b;
+	}
+
+	/* Mix */
+	for (i=0; i<100; i++)
+	{
+		_a5_1_clock(r, 0);
+	}
+
+	/* Output */
+	for (i=0; i<114; i++) {
+		_a5_1_clock(r, 0);
+		if (dl)
+			dl[i] = _a5_1_get_output(r);
+	}
+
+	for (i=0; i<114; i++) {
+		_a5_1_clock(r, 0);
+		if (ul)
+			ul[i] = _a5_1_get_output(r);
+	}
+}
+
+void osmo_a5_1(const uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul)
+{
+	osmo_a5(1, key, fn, dl, ul);
+}
+
+/* ------------------------------------------------------------------------ */
+/* A5/2                                                                     */
+/* ------------------------------------------------------------------------ */
+
+#define A52_R4_CLKBIT0	0x000400
+#define A52_R4_CLKBIT1	0x000008
+#define A52_R4_CLKBIT2	0x000080
+
+/*! GSM A5/2 Clocking function
+ *  \param[in] r Register state
+ *  \param[in] force Non-zero value disable conditional clocking
+ */
+static inline void
+_a5_2_clock(uint32_t r[], int force)
+{
+	int cb[3], maj;
+
+	cb[0] = !!(r[3] & A52_R4_CLKBIT0);
+	cb[1] = !!(r[3] & A52_R4_CLKBIT1);
+	cb[2] = !!(r[3] & A52_R4_CLKBIT2);
+
+	maj = (cb[0] + cb[1] + cb[2]) >= 2;
+
+	if (force || (maj == cb[0]))
+		r[0] = _a5_12_clock(r[0], A5_R1_MASK, A5_R1_TAPS);
+
+	if (force || (maj == cb[1]))
+		r[1] = _a5_12_clock(r[1], A5_R2_MASK, A5_R2_TAPS);
+
+	if (force || (maj == cb[2]))
+		r[2] = _a5_12_clock(r[2], A5_R3_MASK, A5_R3_TAPS);
+
+	r[3] = _a5_12_clock(r[3], A5_R4_MASK, A5_R4_TAPS);
+}
+
+/*! GSM A5/2 Output function
+ *  \param[in] r Register state
+ *  \return The A5/2 output function bit
+ */
+static inline uint8_t
+_a5_2_get_output(uint32_t r[])
+{
+	uint8_t b;
+
+	b = (r[0] >> (A5_R1_LEN-1)) ^
+	    (r[1] >> (A5_R2_LEN-1)) ^
+	    (r[2] >> (A5_R3_LEN-1)) ^
+	    _a5_12_majority( r[0] & 0x08000, ~r[0] & 0x04000,  r[0] & 0x1000) ^
+	    _a5_12_majority(~r[1] & 0x10000,  r[1] & 0x02000,  r[1] & 0x0200) ^
+	    _a5_12_majority( r[2] & 0x40000,  r[2] & 0x10000, ~r[2] & 0x2000);
+
+	return b;
+}
+
+/*! Generate a GSM A5/1 cipher stream
+ *  \param[in] key 8 byte array for the key (as received from the SIM)
+ *  \param[in] fn Frame number
+ *  \param[out] dl Pointer to array of ubits to return Downlink cipher stream
+ *  \param[out] ul Pointer to array of ubits to return Uplink cipher stream
+ *
+ * Either (or both) of dl/ul can be NULL if not needed.
+ */
+void
+_a5_2(const uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul)
+{
+	uint32_t r[4] = {0, 0, 0, 0};
+	uint32_t fn_count;
+	uint32_t b;
+	int i;
+
+	/* Key load */
+	for (i=0; i<64; i++)
+	{
+		b = ( key[7 - (i>>3)] >> (i&7) ) & 1;
+
+		_a5_2_clock(r, 1);
+
+		r[0] ^= b;
+		r[1] ^= b;
+		r[2] ^= b;
+		r[3] ^= b;
+	}
+
+	/* Frame count load */
+	fn_count = osmo_a5_fn_count(fn);
+
+	for (i=0; i<22; i++)
+	{
+		b = (fn_count >> i) & 1;
+
+		_a5_2_clock(r, 1);
+
+		r[0] ^= b;
+		r[1] ^= b;
+		r[2] ^= b;
+		r[3] ^= b;
+	}
+
+	r[0] |= 1 << 15;
+	r[1] |= 1 << 16;
+	r[2] |= 1 << 18;
+	r[3] |= 1 << 10;
+
+	/* Mix */
+	for (i=0; i<99; i++)
+	{
+		_a5_2_clock(r, 0);
+	}
+
+	/* Output */
+	for (i=0; i<114; i++) {
+		_a5_2_clock(r, 0);
+		if (dl)
+			dl[i] = _a5_2_get_output(r);
+	}
+
+	for (i=0; i<114; i++) {
+		_a5_2_clock(r, 0);
+		if (ul)
+			ul[i] = _a5_2_get_output(r);
+	}
+}
+
+void osmo_a5_2(const uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul)
+{
+	osmo_a5(2, key, fn, dl, ul);
+}
+
+/*! Main method to generate a A5/x cipher stream
+ *  \param[in] n Which A5/x method to use
+ *  \param[in] key 8 or 16 (for a5/4) byte array for the key (as received from the SIM)
+ *  \param[in] fn Frame number
+ *  \param[out] dl Pointer to array of ubits to return Downlink cipher stream
+ *  \param[out] ul Pointer to array of ubits to return Uplink cipher stream
+ *  \returns 0 for success, -ENOTSUP for invalid cipher selection.
+ *
+ * Currently A5/[0-4] are supported.
+ * Either (or both) of dl/ul can be NULL if not needed.
+ */
+int
+osmo_a5(int n, const uint8_t *key, uint32_t fn, ubit_t *dl, ubit_t *ul)
+{
+	switch (n)
+	{
+	case 0:
+		if (dl)
+			memset(dl, 0x00, 114);
+		if (ul)
+			memset(ul, 0x00, 114);
+		break;
+
+	case 1:
+		_a5_1(key, fn, dl, ul);
+		break;
+
+	case 2:
+		_a5_2(key, fn, dl, ul);
+		break;
+
+	case 3:
+		_a5_3(key, fn, dl, ul, true);
+		break;
+
+	case 4:
+		_a5_4(key, fn, dl, ul, true);
+		break;
+
+	default:
+		/* a5/[5..7] not supported here/yet */
+		return -ENOTSUP;
+	}
+
+	return 0;
+}
+
+/*! @} */