METHOD FOR THE PROVISION OF DATA SECURITY

Abstract: The present invention concerns a method which makes it possible to sign and/or encrypt a message to be transmitted to a receiver and to reliably ascertain from the message the identity of the sender of the message and the correctness of its contents. In the method, the message is divided into two or more sections. The first section is a header section, to which a sender identification is added. The second section is a data section, to which a check element generated from the contents of the message is appended. Finally, the data section of the messge is signed and/or encrypted so as to allow the sender of the message to be reliably identified. The use of a check element makes it possible to ascertain the correstness of the contents and that the message has been decrypted using the right keys.

Description: METHOD FOR THE PROVISION OF DATA SECURITY FIELD OF THE INVENTION The present invention relates to telecommunication systems. In particular, the invention relates to a new type of method whereby a message to be transmitted to a receiver is signed and/or encrypted. At the same time, the identity of the sender and the correctness of the message can be verified. BACKGROUND OF THE INVENTION Transmitting information as a bit stream from one place to another is easy enough, but it is more difficult to make sure that the information transmitted remains unchanged during the transmission. Cor- respondingly, in an increasing number of cases of data transmission, the sender also wants to make sure that the information transmitted can be received in a usable form only by the party for whom the information was originally intended. To achieve this end, encryp- tion is used. Thus, the purpose of encryption is to ensure that the information will only be useful to the party who possesses the encryption key that allows the message to be decrypted. The strength of encryption is based on the circumstance that computers are not capa- ble of cracking the encryption in a finite length of time . When speaking of messages, reference is primarily made to short messages (SMS, Short Message Service) as used in mobile communication systems, preferably the GSM system (GSM, Global System for Mobile communications). However, 'message' may also refer to a type of message used in any other telecommunication system. Short messages used in a mobile communication system, preferably the GSM system, can be encrypted to ensure that the message will not be visible in plain form to outsiders. The short message is encrypted and a check element is generated from the message using e.g. a hash function. The check element and the encrypted message are transmitted as separate short mes- sages to the receiver. The receiver decrypts the message, and the check element received in the other message is compared with the decrypted data section. In the above-mentioned solution, the problem is that the aggregate of operations, comprising signa- ture and encryption of the message and generation of a check element, has to be transmitted to the receiver in two separate messages, preferably short messages. The object of the present invention is to eliminate the above-mentioned drawbacks or at least to significantly alleviate them. A specific object of the invention is to disclose a new type of method whereby the encryption and/or signature of a message and verification of the identity of the sender of the message and the correct- ness of its contents can be achieved with a single short message. The desired encrypted message together with unequivocal verification data for both sender and receiver is transmitted in a single normal message, preferably a short message in the GSM system. As for the features characteristic of the present invention, reference is made to the claims. BRIEF DESCRIPTION OF THE INVENTION The method of the invention relates to en- cryption and/or signature of a message and to verification of the sender of the message and the correctness of its contents. In the method, the message is divided into two or more sections, said sections comprising at least a header section and a data section. The header section contains information regarding the sender of the message, i.e., it indicates who is the signatory of the message. In a public and private key encryption method, the header section contains data indicating whose public key is needed to decrypt the signature . For the verification of correctness of the contents of the message, a check element is generated from the contents of the data section of the message and appended to the end of the data section. The check element can be generated using a suitable hash function. The verification of correctness of the message is based on the circumstance that both the sender and the receiver of the message use the same hash function. If an attempt is made to decrypt the message using a wrong decryption key, then the check elements will differ from each other. At the same time, the check element functions as a checksum, indicating any errors that may have occurred in the transmission. After the check element has been appended to the data section, the message is encrypted. The encryption method used may be a public and private key method, which produces strong encryption. The encryption algorithm may be e.g. the RSA algorithm (RSA, Rivest, Shamir, Adleman) or any other method that produces strong encryption. The receiver of the message can determine the encryption method in question by an identifier included in the header section of the message. If a public and private key method is used, then the data section of the message is first signed with the sender's secret signing key. When the message is decrypted, the receiver can unequivocally ascertain the identity of the sender as the message is decrypted using the sender's public key. After being signed, the message is encrypted, using e.g. the receiver's public signing key. Thus, only the right receiver, using his/her own secret key, will be able to decipher the encrypted message into plain language. If it is found that the contents of the message differ from what is expected, then the receiver may request retransmission of the message. The method can also be provided with a function whereby an ac- knowledgement of successful transmission is sent to the sender of the message. In the foregoing, encryption and signature of a message have been described with reference to the GSM system. In the GSM system, encryption and/or sig- nature of a message can be accomplished using a mobile station. However, the GSM system is only one preferred example of the system to be used. As compared with prior art, the present invention has the advantage that the signature and/or encryption of a message and the verification of the identity of the sender and the correctness of the contents of the message can be transmitted in a single message, e.g. a short message as used in the GSM system. A further advantage is that the key used by the signatory of the message can be identified by only five bytes. LIST OF ILLUSTRATIONS In the following, the invention will be de- scribed in detail by the aid of a few examples of its embodiments, wherein Fig. 1 represents a preferred method according to the present invention, and Fig. 2 illustrates the generation of an iden- tifier to be included in the header section in the method presented in Fig. 1. Fig. 1 shows the structure of a signed and encrypted SMS message. In this example, a public and private key method and the RSA algorithm are used. Ac- cording to the invention, the header section 1 of the message contains an identifier (MUI , Mobile User Identification) of the sender, i.e. signatory of the mes- sage. The length of the header section is 12 bytes, i.e. 96 bits. Appended to the end of the data section 2 is a MD_5 check element, which has a length of 16 bytes. The check element is generated on the basis of the contents of the data section 2 using a hash function, which in this example is MD5 (MD, Message Digest) . In the next step, the data section 2 is signed using the sender's secret signing key. As a result, a data section 4 signed by the sender is produced. The MUI(PidKey) field in the header section 3 now contains the identification of the signatory of the message. The sender identification MUI (PidKey) is a five-byte field. The identifier indicates whose public signing is to be used to decrypt and verify the signature. The receiver may already know the public key or he may request it from a TTP (Trusted Third Party) . In the next step, the header section 3 remains unchanged, whereas the data section 4 is additionally encrypted with the receiver's public key. As a result, a data section 6 is produced which has been both signed and encrypted. The above-mentioned operations make it possible to verify the authenticity of the sender and the contents of the data section. In conformity with the short message standard of the GSM system, the total length of the message is 140 bytes (160 characters) . Fig. 2 illustrates the generation of the MUI (PidKey) identifier included in the header section of the message presented in Fig. 1. The identification part to be generated is associated with a given name (block 21) . From the aggregate formed by the name, the sender's public signing key (length about 160 bits) and a 1024 -bit modulus (block 22) , a hash code is generated by using a hash function. The hash function used may be e.g. SHA1 (SHA, Secure Hashing Algorithm) or MD5. The hashing produces a 20-byte field (block 23). The MUI (PidKey) identifier (block 24) is formed by taking the last five bytes of the hashed identifier. The invention is not restricted to the examples of its embodiments described above, but many variations are possible within the scope of the inventive idea defined in the claims.

Claims: CLAIMS 1. Method for the signature and/or encryption of a message and verification of authenticity of the sender of the message and correctness of its contents, in which method the message is divided into two or more sections, said sections comprising at least a header section and an actual data section, in which method a message is generated and transmitted in an encrypted form to a specified receiver, c h a r a c - t eri z ed in that the method comprises the steps of: generating from the contents of the message a check element, which is appended to the end of the data section; adding sender identification data to the header section of the message; and encrypting and/or signing the data section of the message by an encryption method that allows reliable identification of the receiver and sender of the mes- sage. 2. Method as defined in claim 1, char ac t e r i z ed in that the check element to be appended to the end of the data section is generated by using a hash function. 3. Method as defined in claims 1 and 2, charact eri zed in that the message is signed and/or encrypted using a public and private key method. 4. Method as defined in claims 1 - 3, charact eri zed in that the encryption algorithm used is the RSA algorithm or a corresponding algorithm producing strong encryption. 5. Method as defined in claims 1 - 4, charact eri zed in that the encryption method used is determined from an identifier added to the header section of the message. 6. Method as defined in claims 1 - 5, charac t e ri zed in that sender identification data is added to the header section of the message, letting the receiver know whose public signing key is to be used to decrypt and verify the signature. 7. Method as defined in claims 1 - 6, charact eri zed in that the data section of the message is signed with a digital signature. 8. Method as defined in claims 1 - 7, charac t eri zed in that the data section of the message is signed using the sender's secret signing key. 9. Method as defined in claims 1 - 8, charact e ri zed in that the data section of the message, having been encrypted with the sender's public signing key, is encrypted with the receiver's public encryption key. 10. Method as defined in claims 1 - 9, charact eri zed in that the received message is decrypted using the receiver's secret key. 11. Method as defined in claims 1 - 10, charact e ri zed in that the sender of the message is ascertained by decrypting the received message again using the sender's public signing key. 12. Method as defined in claims 1 - 11, characteri zed in that the correctness of the decrypted message is ascertained on the basis of the check element included in the data section of the message. 13. Method as defined in claims 1 - 12, charac t eri zed in that, if errors are detected in the contents of the message, then retransmission of the message is requested. 14. Method as defined in claims 1 - 13, charact eri zed in that an acknowledgement of successful transmission of the message is received. 15. Method as defined in claims 1 - 14, charac t eri zed in that the encryption of a message and verification of the sender and contents of the message are applied in a mobile communication system, e.g. the GSM system. 16. Method as defined in claims 1 - 15, charac t eri zed in that the message is signed and/or encrypted using a mobile station.

Inventors: HILTUNEN MATTI, LIUKKONEN JUKKA, VATANEN HARRI, HILTUNEN, MATTI, LIUKKONEN, JUKKA, VATANEN, HARRI
Applicants: HILTUNEN MATTI, LIUKKONEN JUKKA, SONERA SMARTTRUST OY, VATANEN HARRI, HILTUNEN, MATTI, LIUKKONEN, JUKKA, VATANEN, HARRI
Application year: 2000
Main classification: H04L9
IPC codes: H04L9