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/* Copyright 2020 sysmocom s.f.m.c. GmbH
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* SPDX-License-Identifier: Apache-2.0 */
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package org.osmocom.IMSIPseudo;
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public class MobileIdentity {
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public static final byte MI_IMSI = 1;
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/* Convert BCD-encoded digit into printable character
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* \param[in] bcd A single BCD-encoded digit
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* \returns single printable character
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*/
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public static byte bcd2char(byte bcd)
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{
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if (bcd < 0xa)
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return (byte)('0' + bcd);
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else
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return (byte)('A' + (bcd - 0xa));
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}
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/* Convert BCD to string.
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* The given nibble offsets are interpreted in BCD order, i.e. nibble 0 is bcd[0] & 0xf, nibble 1 is bcd[0] >> 4, nibble
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* 3 is bcd[1] & 0xf, etc..
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* \param[out] dst Output byte array.
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* \param[in] dst_ofs Where to start writing in dst.
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* \param[in] dst_len How many bytes are available at dst_ofs.
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* \param[in] bcd Binary coded data buffer.
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* \param[in] start_nibble Offset to start from, in nibbles.
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* \param[in] end_nibble Offset to stop before, in nibbles.
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* \param[in] allow_hex If false, return false if there are digits other than 0-9.
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* \returns true on success, false otherwise
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*/
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public static boolean bcd2str(byte dst[], byte dst_ofs, byte dst_len,
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byte bcd[], byte start_nibble, byte end_nibble, boolean allow_hex)
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{
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byte nibble_i;
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byte dst_i = dst_ofs;
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byte dst_end = (byte)(dst_ofs + dst_len);
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boolean rc = true;
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for (nibble_i = start_nibble; nibble_i < end_nibble && dst_i < dst_end; nibble_i++, dst_i++) {
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byte nibble = bcd[(byte)nibble_i >> 1];
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if ((nibble_i & 1) != 0)
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nibble >>= 4;
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nibble &= 0xf;
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if (!allow_hex && nibble > 9)
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rc = false;
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dst[dst_i] = bcd2char(nibble);
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}
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return rc;
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}
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public static byte[] mi2str(byte mi[])
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{
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/* The IMSI byte array by example:
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* 08 99 10 07 00 00 10 74 90
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*
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* This is encoded according to 3GPP TS 24.008 10.5.1.4 Mobile
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* Identity, short the Mobile Identity IEI:
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*
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* 08 length for the following MI, in bytes.
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* 9 = 0b1001
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* 1 = odd nr of digits
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* 001 = MI type = IMSI
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* 9 first IMSI digit (BCD)
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* 0 second digit
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* 1 third
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* ...
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* 0 14th digit
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* 9 15th and last digit
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*
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* If the IMSI had an even number of digits:
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*
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* 08 98 10 07 00 00 10 74 f0
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*
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* 08 length for the following MI, in bytes.
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* 8 = 0b0001
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* 0 = even nr of digits
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* 001 = MI type = IMSI
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* 9 first IMSI digit
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* 0 second digit
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* 1 third
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* ...
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* 0 14th and last digit
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* f filler
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*/
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byte bytelen = mi[0];
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byte mi_type = (byte)(mi[1] & 0xf);
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boolean odd_nr_of_digits = ((mi_type & 0x08) != 0);
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byte start_nibble = 2 + 1; // 2 to skip the bytelen, 1 to skip the mi_type
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byte end_nibble = (byte)(2 + bytelen * 2 - (odd_nr_of_digits ? 0 : 1));
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byte str[] = new byte[end_nibble - start_nibble];
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bcd2str(str, (byte)0, (byte)str.length, mi, start_nibble, end_nibble, true);
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return str;
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}
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public static byte char2bcd(byte c)
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{
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if (c >= '0' && c <= '9')
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return (byte)(c - '0');
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else if (c >= 'A' && c <= 'F')
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return (byte)(0xa + (c - 'A'));
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else if (c >= 'a' && c <= 'f')
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return (byte)(0xa + (c - 'a'));
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else
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return 0;
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}
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public static byte[] str2mi(byte str[], byte mi_type, byte min_buflen)
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{
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boolean odd_digits = ((str.length & 1) != 0);
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/* 1 nibble of mi_type.
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* str.length nibbles of MI BCD.
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*/
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byte mi_nibbles = (byte)(1 + str.length);
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byte mi_bytes = (byte)(mi_nibbles / 2 + ((mi_nibbles & 1) != 0? 1 : 0));
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/* 1 byte of total MI length in bytes, plus the MI nibbles */
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byte buflen = (byte)(1 + mi_bytes);
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/* Fill up with 0xff to the requested buffer size */
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if (buflen < min_buflen)
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buflen = min_buflen;
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byte buf[] = new byte[buflen];
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for (byte i = 0; i < buf.length; i++)
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buf[i] = (byte)0xff;
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/* 1 byte of following MI length in bytes */
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buf[0] = mi_bytes;
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/* first MI byte: low nibble has the MI type and odd/even indicator bit,
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* high nibble has the first BCD digit.
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*/
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mi_type = (byte)(mi_type & 0x07);
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if (odd_digits)
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mi_type |= 0x08;
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buf[1] = (byte)((char2bcd(str[0]) << 4) + mi_type);
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/* fill in the remaining MI nibbles */
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byte str_i = 1;
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for (byte mi_i = 1; mi_i < mi_bytes; mi_i++) {
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byte data = char2bcd(str[str_i++]);
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if (str_i < str.length)
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data |= char2bcd(str[str_i++]) << 4;
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else
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data |= 0xf0;
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buf[1 + mi_i] = data;
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}
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return buf;
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}
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}
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