Method and apparatus for encrypting a security key in a mobile communication terminal

0001The present invention relates generally to an apparatus and method for storing security keys in a mobile communication terminal, and in particular, to an apparatus and method for encrypting and storing security keys in a mobile communication terminal so as to prevent unauthorized use of the security keys.

0002In general, a Universal Mobile Telecommunications System/Global System for Mobile communication (UMTS/GSM) system provides a personalization function for allowing a specific terminal to use only a specific Subscriber Identity Module (SIM) card. Examples of the personalization are network personalization, network subset personalization, service provider personalization, corporate personalization, and SIM/USIM (Universal SIM) personalization that are defined in the 3rd Generation Partnership Project (3GPP).

0003The personalization function allows a specific terminal to use only a specific SIM card, by using an International Mobile Station Identity (IMSI), a General IDentifier 1 (GID 1) or a GID 2 that is stored in the SIM card.

0004When a personalization function is enabled in a mobile communication terminal, the use of a SIM card is restricted. A prestored control key is used to disable the personalization function of the mobile communication terminal, i.e., to remove the restrictions on the use of the SIM card. The control key is randomly generated using the seed of a process program, and the generated control key is stored in the memory of the mobile communication terminal in the form of a decimal number. The seed of the process program is used to randomly generate not only the control key but also security keys that are used for receiving services such as e-mail and mobile banking.

0005Recently, hackers have been successful in their attempt to compromise the security of the Internet, thus leading to unauthorized use of the security keys (e.g., control keys) of mobile communication terminals and service providers. Security programs such as the 128-bit Advanced Encryption Standard (AES) algorithm, has been developed to prevent the unauthorized use of the security keys.

0006A conventional mobile communication terminal generates a security key using the conventional security program and stores the generated security key in its memory. However, the conventional security program merely enhances the security effects on the generation of the security key. Therefore, it is still possible to easily obtain the security key by illegally accessing and dumping the mobile terminal memory. This causes the unauthorized use of the security key and the mobile communication terminal.

0007According to <patcit id="pcit0001" dnum="GB2376386A"><text>GB 2 376 386 A</text></patcit>, a second unit of memory may include a password. This password is used by an ASIC when the user of a mobile telephone unlocks the access control system for a specific network. To do this, the user types on the keypad a password value. This password value is then compared within the ASIC with the password value contained in the memory unit which has been decrypted previously using a cipher key

0008The document "Digital cellular telecommunications system (Phase 2+); Personalization of GSM Mobile Equipment (ME); Mobile functionality specification (GSM 02.22 version 6.0.0 Release 1997)"; TS 101 624 of the European Telecommunications Standards Institute, 1999, mentions that the network personalization feature is controlled by a network control key (NCK) which has to be entered into the mobile equipment in order to network depersonalize it. The network personalization process comprises that the NCK is stored in the mobile equipment. To depersonalize the mobile equipment, the correct NCK shall be entered. If the entered NCK is the same as the one stored in the mobile equipment, the network personalization indicator is set to "OFF". The NCK should be randomly selected or pseudo-randomly generated and differ from mobile equipment to mobile equipment.

0009<patcit id="pcit0002" dnum="US6799155B1"><text>US 6,799,155 B1</text></patcit> deals with the replacement of externally mounted user interface modules with software emulation of user interface module functions in embedded processor applications and teaches storing of key information in encrypted form.

0010According to <patcit id="pcit0003" dnum="EP0565506A2"><text>EP 0 565 506 A2</text></patcit>, in a typical CDMA system, the informational datastream to be transmitted is impressed upon a much higher bit rate data stream generated by a pseudo-random code generator. This combination of higher bit rate signal with the lower bit rate datastream is called coding or spreading the informational datastream signal. A plurality of coded information signals are transmitted on radio frequency carrier waves and jointly received as a composite signal at a receiver. By correlating the composite signal with one of the unique spreading codes, the corresponding information signal is isolated and decoded. The encoding of individual information signals is simplified by encoding each signal with a common block error-correction code, which may be readily decoded using a correlation device such as a Fast Walsh Transform circuit. At the system level, a pseudo-randomly generated code key is used to select one of the scrambling masks common to all of the mobile stations in a particular cell. At the subscriber level, a pseudo-randomly generated ciphering key enciphers individual information signals before the scrambling operation.

0011The present invention has been designed to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, the object of the present invention is to provide an apparatus and method for preventing unauthorized use of a security key in a mobile communication terminal.

0012This object is solved by the subject matter of the independent claims.

0013Preferred embodiments are defined in the dependent claims.

0014The present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIG. 1</figref> is a block diagram of a mobile communication terminal according to the present invention;</li><li><figref idref="f0002">FIG. 2</figref> is a block diagram of a control key encryptor according to the present invention;</li><li><figref idref="f0003">FIG. 3</figref> is a flowchart illustrating a procedure for encrypting a control key according to the present invention; and</li><li><figref idref="f0004">FIG 4</figref> is a flowchart illustrating a procedure for disabling personalization of a SIM card according to the present invention.</li></ul>

0015Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

0016The present invention provides an apparatus and method for encrypting and storing security keys in a mobile communication terminal, with the aim to prevent unauthorized use of the security keys by memory dump. Security keys refer to keys that are randomly generated by a process program for the security of the mobile communication terminal. In the following description, a control key for disabling personalization of a SIM card is taken as an example of the security key.

0017Examples of a mobile communication terminal are a cellular phone, a personal communication system (PCS) terminal, a personal data assistant (PDA), an international mobile telecommunications-2000 (IMT-2000) terminal, and a fourth generation (4G) broadband communication terminal. The following description is made in terms of a general structure of the above communication terminals.

0018Referring to <figref idref="f0001">FIG. 1</figref>, the mobile communication terminal includes a controller 100, a SIM card 102, a memory unit 104, a display unit 110, a keypad 108, a communication module 110, an audio processor 112, a speaker, a microphone, and an antenna. The controller 100 includes a control key encryptor 114.

0019Controller 100 controls the overall operation of the mobile communication terminal. For example, controller 100 processes and controls voice communication and data communication. In addition, using control key encryptor 114, controller 100 randomly generates a control key, encrypts the random control key, and stores the encrypted control key in memory unit 104.

0020SIM card 102 is an attachment to the mobile communication terminal. SIM card 102 includes a microprocessor and a memory chip and stores a variety of user data.

0021Memory unit 104 stores the program for controlling the overall operation of the mobile communication terminal, temporary data generated during the operation of the mobile communication terminal, system parameters, and a variety of updatable data such as phone book and short message service (SMS) message. In addition, memory unit 104 stores the encrypted control key. At this point, the control key is stored in the non-volatile area of memory unit 104.

0022Display unit 106 displays status information generated during an operation of the mobile terminal, characters inputted by a user, moving pictures, still pictures, and so on.

0023Keypad 108 includes numeric keys of digits 0-9 and a plurality of function keys, such as, a Talk key, Navigation keys (▲ / <b>▼</b>/ ◄ / ► ), and a Confirmation key. Keypad 108 provides controller 100 with key input data that corresponds to a key pressed by the user.

0024Communication module 110 processes radio-frequency (RF) signals that are transmitted/received through the antenna. Audio processor 112 connected to controller 100, and the speaker and the microphone connected to audio processor 112 constitute an audio input/output block that is used for voice communication.

0025Referring to <figref idref="f0002">FIG 2</figref>, control key encryptor 114 includes a control key generator 201, a bit converter 203, and a spreader 205.

0026Using a process program, control key generator 201 generates the control key randomly. The generated control key is an 8-digit number expressed as Equation (1): <maths id="math0001" num="(1)"><math display="block"><mi mathvariant="italic">Control Key</mi><mo mathvariant="italic">=</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">0</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">1</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">2</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">3</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">4</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">5</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">6</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">7</mn></msub></math><img file="EP1863301B1_D0001.tif" /></maths> where <i>C_i</i> denotes the i^th code of the control key and is a decimal number.

0027Bit converter 203 converts the generated decimal control key from control key generator 201 into a bit-format expressed as Equation(2) by a bitwise operation: <maths id="math0002" num="(2)"><math display="block"><mtable><mtr><mtd><mtable><mtr><mtd><msub><mi>C</mi><mn mathvariant="italic">0</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">00</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">01</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">02</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">03</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">04</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">05</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">06</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">07</mn></msub></mtd></mtr><mtr><mtd><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">1</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">10</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">11</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">12</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">13</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">14</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">15</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">16</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">17</mn></msub></mtd></mtr><mtr><mtd><msub><mi>C</mi><mn mathvariant="italic">2</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">20</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">21</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">22</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">23</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">24</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">25</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">26</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">27</mn></msub></mtd></mtr><mtr><mtd><msub><mi>C</mi><mn mathvariant="italic">3</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">30</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">31</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">32</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">33</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">34</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">35</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">36</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">37</mn></msub></mtd></mtr><mtr><mtd><msub><mi>C</mi><mn mathvariant="italic">4</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">40</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">41</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">42</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">43</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">44</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">45</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">46</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">47</mn></msub></mtd></mtr><mtr><mtd><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">5</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">50</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">51</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">52</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">53</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">54</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">55</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">56</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">57</mn></msub></mtd></mtr><mtr><mtd><msub><mi>C</mi><mn mathvariant="italic">6</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">60</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">61</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">62</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">63</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">64</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">65</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">66</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">67</mn></msub></mtd></mtr><mtr><mtd><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">7</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">70</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">71</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">72</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">73</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">74</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">75</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">76</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">77</mn></msub></mtd></mtr></mtable></mtd></mtr></mtable></math><img file="EP1863301B1_D0002.tif" /></maths> where <i>b_ij</i> denotes the <i>j</i>^th bit of the <i>i</i>^h code of the control key.

0028Using an orthogonal Walsh code expressed as Expression (3) below, spreader 205 spreads the bits of the control key into random data expressed as Equation (3) and Equation (4). <maths id="math0003" num="(3)"><math display="block"><mi mathvariant="italic">Wlash code</mi><mo mathvariant="italic">=</mo><mfenced open="[" close="]"><msub><mi mathvariant="italic">W</mi><mn mathvariant="italic">0</mn></msub><mo>⁢</mo><msub><mi mathvariant="italic">W</mi><mn mathvariant="italic">1</mn></msub><mo>⁢</mo><msub><mi mathvariant="italic">W</mi><mn mathvariant="italic">2</mn></msub><mo>⁢</mo><msub><mi mathvariant="italic">W</mi><mn mathvariant="italic">3</mn></msub><mo>⁢</mo><msub><mi mathvariant="italic">W</mi><mn mathvariant="italic">4</mn></msub><mo>⁢</mo><msub><mi mathvariant="italic">W</mi><mn mathvariant="italic">5</mn></msub><mo>⁢</mo><msub><mi mathvariant="italic">W</mi><mn mathvariant="italic">6</mn></msub><mo>⁢</mo><msub><mi mathvariant="italic">W</mi><mn mathvariant="italic">7</mn></msub></mfenced></math><img file="EP1863301B1_D0003.tif" /></maths> where <i>W_i</i> denotes the <i>i</i>^th Walsh code that is represented in the form of a row vector, and said code has a length of 8. <maths id="math0004" num="(4)"><math display="block"><mtable columnalign="left"><mtr><mtd><mtable><mtr><mtd><msub><mi mathvariant="italic">S</mi><mn mathvariant="italic">0</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">00</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">01</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">02</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">03</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">04</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">05</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">06</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">07</mn></msub></mtd></mtr><mtr><mtd><msub><mi mathvariant="italic">S</mi><mn mathvariant="italic">1</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">10</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">11</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">12</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">13</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">14</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">15</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">16</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">17</mn></msub></mtd></mtr><mtr><mtd><msub><mi mathvariant="italic">S</mi><mn mathvariant="italic">2</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">20</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">21</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">22</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">23</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">24</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">25</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">26</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">27</mn></msub></mtd></mtr><mtr><mtd><msub><mi mathvariant="italic">S</mi><mn mathvariant="italic">3</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">30</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">31</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">32</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">33</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">34</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">35</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">36</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">37</mn></msub></mtd></mtr><mtr><mtd><msub><mi mathvariant="italic">S</mi><mn mathvariant="italic">4</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">40</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">41</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">42</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">43</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">44</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">45</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">46</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">47</mn></msub></mtd></mtr><mtr><mtd><msub><mi mathvariant="italic">S</mi><mn mathvariant="italic">5</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">50</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">51</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">52</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">53</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">54</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">55</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">56</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">57</mn></msub></mtd></mtr><mtr><mtd><msub><mi mathvariant="italic">S</mi><mn mathvariant="italic">6</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">60</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">61</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">62</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">63</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">64</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">65</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">66</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">67</mn></msub></mtd></mtr><mtr><mtd><msub><mi mathvariant="italic">S</mi><mn mathvariant="italic">7</mn></msub><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">70</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">71</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">72</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">73</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">74</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">75</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">76</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">77</mn></msub></mtd></mtr></mtable></mtd></mtr><mtr><mtd><mi mathvariant="italic">E</mi><mo mathvariant="italic">:</mo><msub><mi mathvariant="italic">e</mi><mn mathvariant="italic">0</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">e</mi><mn mathvariant="italic">1</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">e</mi><mn mathvariant="italic">2</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">e</mi><mn mathvariant="italic">3</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">e</mi><mn mathvariant="italic">4</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">e</mi><mn mathvariant="italic">5</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">e</mi><mn mathvariant="italic">6</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">e</mi><mn mathvariant="italic">7</mn></msub></mtd></mtr></mtable></math><img file="EP1863301B1_D0004.tif" /></maths> where S<i>_i</i> denotes diffused random data of the <i>i</i>^th code of the control key, s<i>_ij</i> denotes a Walsh-spread random value of the j^th bit of the <i>i</i>^th code of the control key, and <i>E</i> denotes a row vector of random data generated by Walsh-spreading the control key.

0029The <i>s_ij</i> can be calculated using EquationExpression (5) below and the e_i can be calculated using Equation (6) below. <maths id="math0005" num="(5)"><math display="block"><mtable><mtr><mtd><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">00</mn></msub><mo mathvariant="italic">=</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">00</mn></msub><mo mathvariant="italic">•</mo><msub><mi mathvariant="italic">W</mi><mn mathvariant="italic">0</mn></msub></mtd></mtr><mtr><mtd><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">01</mn></msub><mo mathvariant="italic">=</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">01</mn></msub><mo mathvariant="italic">•</mo><msub><mi mathvariant="italic">W</mi><mn mathvariant="italic">0</mn></msub></mtd></mtr><mtr><mtd><mo mathvariant="italic">⋮</mo></mtd></mtr><mtr><mtd><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">70</mn></msub><mo mathvariant="italic">=</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">70</mn></msub><mo mathvariant="italic">•</mo><msub><mi mathvariant="italic">W</mi><mn mathvariant="italic">7</mn></msub></mtd></mtr><mtr><mtd><msub><mi mathvariant="italic">s</mi><mn mathvariant="italic">71</mn></msub><mo mathvariant="italic">=</mo><msub><mi mathvariant="italic">b</mi><mn mathvariant="italic">71</mn></msub><mo mathvariant="italic">•</mo><msub><mi mathvariant="italic">W</mi><mn mathvariant="italic">7</mn></msub></mtd></mtr></mtable></math><img file="EP1863301B1_D0005.tif" /></maths><maths id="math0006" num="(5)"><math display="block"><mn>.....</mn><mfenced><mn>5</mn></mfenced></math><img file="EP1863301B1_D0006.tif" /></maths> where s<i>_ij</i> denotes a Walsh-spread random value of the <i>j</i>^th bit of the <i>i</i>^th code of the control key, <i>b_ij</i> denotes the <i>j</i>^th bit of the <i>i</i>^th code of the control key, and <i>W_i</i> denotes the <i>i</i>^th Walsh code <maths id="math0007" num="(6)"><math display="block"><msub><mi>e</mi><mi>i</mi></msub><mo>=</mo><msub><mi>s</mi><mrow><mn>0</mn><mo>⁢</mo><mi>i</mi></mrow></msub><mo>+</mo><msub><mi>s</mi><mrow><mn>1</mn><mo>⁢</mo><mi>i</mi></mrow></msub><mo>+</mo><mo>…</mo><mo>+</mo><msub><mi>s</mi><mrow><mn>7</mn><mo>⁢</mo><mi>i</mi></mrow></msub></math><img file="EP1863301B1_D0007.tif" /></maths> where <i>S_ij</i> denotes a Walsh-spread random value of the <i>j</i>^th bit of the <i>i</i>^th code of the control key.

0030Spreader 205 provides memory unit 104 with the random data <i>E</i> generated by Equation (4).

0031Referring to <figref idref="f0003">FIG. 3</figref>, controller 100 executes a program to generate a control key that is used to disable personalization of a SIM card, in step 301.

0032In step 303, controller 100 generates a random control key. The random control key is a decimal number expressed as Equation (1).

0033In step 305, controller 100 converts the decimal random key into a bit-format expressed as Equation (2).

0034In step 307, controller 100 spreads the bit-format control key using the Walsh code. The orthogonal Walsh code expressed as Equation (3) is used to spread the bit-format control key into random data expressed as Equation (4).

0035In step 309, controller 100 stores the spread random data in memory unit 104. Thereafter, controller 100 ends the procedure.

0036As described above, controller 100 generates the random control key, the orthogonal Walsh code is used to spread the random control key into the random data, and the random data is stored in memory unit 104. Therefore, even if memory unit 104 is illegally accessed and dumped to read the stored control key, an accurate control key cannot be detected without the use of accurate Walsh covering.

0037Referring to <figref idref="f0004">FIG. 4</figref>, controller 100 detects if a SIM card personalization disable mode is selected.

0038If the SIM card personalization disable mode is selected, controller 100 detects if an encrypted control key is stored in memory unit 104, in step 403.

0039In step 405, controller 100 decrypts the encrypted control key using the Walsh code index expressed as Equation (7): <maths id="math0008" num="(7)"><math display="block"><mn>01234567</mn><mo>=</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">0</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">1</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">2</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">3</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">4</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">5</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">6</mn></msub><mo mathvariant="italic">,</mo><msub><mi mathvariant="italic">C</mi><mn mathvariant="italic">7</mn></msub></math><img file="EP1863301B1_D0008.tif" /></maths> where "01234567"denotes a Walsh code index that is used to perform a Walsh covering operation for decrypting the codes of the control key, and "<i>C_i</i>" denotes a control key that is to be compared with a control key (<i>C'_i</i>) decrypted using the Walsh code index.

0040For example, in order to decrypt the first code <i>C₀</i> of the control key, the random data <i>E</i> stored in memory unit 104 is multiplied by the first Walsh code index '0' as expressed by Equation (8) below. <maths id="math0009" num="(8)"><math display="block"><mi mathvariant="italic">b</mi><mo>⁢</mo><mn mathvariant="italic">0</mn><mo>⁢</mo><mi mathvariant="italic">iʹ</mi><mo mathvariant="italic">=</mo><mi mathvariant="italic">E</mi><mo mathvariant="italic">•</mo><msub><mi mathvariant="italic">W</mi><mn mathvariant="italic">0</mn></msub></math><img file="EP1863301B1_D0009.tif" /></maths> where b<i>_0i</i> denotes the <i>i</i>^th bit of the first code of the control key, <i>E</i> denotes the random data (i.e., the encrypted control key) stored in memory unit 104, and <i>W₀</i> denotes the first Walsh code index. Because the Walsh codes are orthogonal to one another, they have a value of 0 if Walsh codes other than those for Walsh code spreading are used. Therefore, it is possible to decrypt only a value for the corresponding Walsh code index.

0041As shown in Equation (8), the eight bits of the first code of the control key are recovered using the Walsh covering operation. When the recovered eight bits are converted into a decimal number, the first code <i>C_o' of</i> the control key is recovered.

0042In the above way, all the encrypted control keys are decrypted using the Walsh code index. In step 407, the decrypted control key <i>(C'₀, C'₁, C'₂, C'₃, C'₄, C'₅, C₆ C'₇)</i> is compared with the control key <i>(Co, C₁, C₂, C₃, C₄, C₅, C₆,</i> C₇). If the decrypted control key is identical to the control key, controller 100 depersonalizing (unlocking) the personalization of the SIM card and then ends the procedure. On the other hand, if the decrypted control key is different from the control key, the controller ends the procedure maintaining the personalization of the SIM card.

0043As described above, the security keys generated by the process program is encrypted and stored in the mobile communication terminal. Therefore, even if the stored security keys are read by hacking or memory dump, it is impossible to detect the accurate security keys. Accordingly, it is possible to prevent the unauthorized use of the mobile communication terminal.

0044While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as further defined by the appended claims.