• Attacks on A5/1 as used in GSM. In 2003, Barkan et al. Published several attacks on GSM encryption. The first is an active attack. GSM phones can be convinced to use the much weaker A5/2 cipher briefly. A5/2 can be broken easily, and the phone uses the same key as for the stronger A5/1 algorithm.
• Jan 04, 2018 DES algorithm follows the Feistel Structure Most of the Block cipher algorithms follows Feistel Structure BLOCK SIZE - 64 bits Plain Text No. Of Rounds - 16 Rounds Key Size - 64 bits Sub Key Size.

• GSM Tutorial

• GSM Useful Resources

Oct 21, 2016  The encryption scheme used for second generation (2G) mobile phone data can be hacked within seconds by exploiting weaknesses and using common hardware, A.STAR.

• Selected Reading

https://newinteractive833.weebly.com/blog/auto-click-free-download-mac. GSM is the most secured cellular telecommunications system available today. GSM has its security methods standardized. GSM maintains end-to-end security by retaining the confidentiality of calls and anonymity of the GSM subscriber.

Gsm Key Generation And Encryption Processor

Temporary identification numbers are assigned to the subscriber’s number to maintain the privacy of the user. The privacy of the communication is maintained by applying encryption algorithms and frequency hopping that can be enabled using digital systems and signalling.

This chapter gives an outline of the security measures implemented for GSM subscribers.

Mobile Station Authentication

The GSM network authenticates the identity of the subscriber through the use of a challenge-response mechanism. A 128-bit Random Number (RAND) is sent to the MS. The MS computes the 32-bit Signed Response (SRES) based on the encryption of the RAND with the authentication algorithm (A3) using the individual subscriber authentication key (Ki). Upon receiving the SRES from the subscriber, the GSM network repeats the calculation to verify the identity of the subscriber.

The individual subscriber authentication key (Ki) is never transmitted over the radio channel, as it is present in the subscriber's SIM, as well as the AUC, HLR, and VLR databases. If the received SRES agrees with the calculated value, the MS has been successfully authenticated and may continue. If the values do not match, the connection is terminated and an authentication failure is indicated to the MS.

The calculation of the signed response is processed within the SIM. It provides enhanced security, as confidential subscriber information such as the IMSI or the individual subscriber authentication key (Ki) is never released from the SIM during the authentication process.

Signalling and Data Confidentiality

The SIM contains the ciphering key generating algorithm (A8) that is used to produce the 64-bit ciphering key (Kc). This key is computed by applying the same random number (RAND) used in the authentication process to ciphering key generating algorithm (A8) with the individual subscriber authentication key (Ki).

GSM provides an additional level of security by having a way to change the ciphering key, making the system more resistant to eavesdropping. The ciphering key may be changed at regular intervals as required. As in case of the authentication process, the computation of the ciphering key (Kc) takes place internally within the SIM. Therefore, sensitive information such as the individual subscriber authentication key (Ki) is never revealed by the SIM.

Encrypted voice and data communications between the MS and the network is accomplished by using the ciphering algorithm A5. Encrypted communication is initiated by a ciphering mode request command from the GSM network. Upon receipt of this command, the mobile station begins encryption and decryption of data using the ciphering algorithm (A5) and the ciphering key (Kc).

Subscriber Identity Confidentiality

To ensure subscriber identity confidentiality, the Temporary Mobile Subscriber Identity (TMSI) is used. Once the authentication and encryption procedures are done, the TMSI is sent to the mobile station. After the receipt, the mobile station responds. The TMSI is valid in the location area in which it was issued. For communications outside the location area, the Location Area Identification (LAI) is necessary in addition to the TMSI.

End-to-end encryption (E2EE) is a system of communication where only the communicating users can read the messages. In principle, it prevents potential eavesdroppers – including telecom providers, Internet providers, and even the provider of the communication service – from being able to access the cryptographic keys needed to decrypt the conversation.^[1]

In many messaging systems, including email and many chat networks, messages pass through intermediaries and are stored by a third party, from which they are retrieved by the recipient. Even if the messages are encrypted, they are typically only encrypted 'in transit', and are stored in decrypted form by the third party. This allows the third party to provide search and other features, or to scan for illegal and unacceptable content, but also means they can be read and misused by anyone who has access to the stored messages on the third party system, whether this is by design or via a backdoor. This can be seen as a concern in many cases where privacy is very important, such as persons living under repressive governments, whistleblowing, mass surveillance, businesses whose reputation depends on its ability to protect third party data, negotiations and communications that are important enough to have a risk of targeted 'hacking', and where sensitive subjects such as health, and information about minors are involved.

End-to-end encryption is intended to prevent data being read or secretly modified, other than by the true sender and recipient(s). The messages are encrypted by the sender but the third party does not have a means to decrypt them, and stores them encrypted. The recipient retrieves the encrypted data and decrypts it themselves.

Because no third parties can decipher the data being communicated or stored, for example, companies that use end-to-end encryption are unable to hand over texts of their customers' messages to the authorities.^[2]

Key exchange[edit]

In an E2EE system, encryption keys must only be known to the communicating parties. To achieve this goal, E2EE systems can encrypt data using a pre-arranged string of symbols, called a pre-shared secret (PGP), or a one-time secret derived from such a pre-shared secret (DUKPT). They can also negotiate a secret key on the spot using Diffie-Hellman key exchange (OTR).^[3]

Modern usage[edit]

As of 2016, typical server-based communications systems do not include end-to-end encryption. These systems can only guarantee the protection of communications between clients and servers, meaning that users have to trust the third parties who are running the servers with the original texts. End-to-end encryption is regarded as safer because it reduces the number of parties who might be able to interfere or break the encryption.^[4] In the case of instant messaging, users may use a third-party client to implement an end-to-end encryption scheme over an otherwise non-E2EE protocol.^[5]

Some non-E2EE systems, such as Lavabit and Hushmail, have described themselves as offering 'end-to-end' encryption when they did not.^[6] Other systems, such as Telegram and Google Allo, have been criticized for not having end-to-end encryption, which they offer, enabled by default. Telegram did not enable end-to-end encryption by default on VoIP calls while users were using desktop software version, but that problem was fixed quickly.^[7][8]

Some encrypted backup and file sharing services provide client-side encryption. The encryption they offer is here not referred to as end-to-end encryption, because the services are not meant for sharing messages between users. However, the term 'end-to-end encryption' is often used as a synonym for client-side encryption.^{[citation needed]}

The term 'end-to-end encryption' originally only meant that the communication is never decrypted during its transport from the sender to the receiver.^[9]For example, around 2003, E2EE has been proposed as an additional layer of encryption for GSM^[10] or TETRA^[11], in addition to the existing radio encryption protecting the communication between the mobile device and the network infrastructure. This has been standardised by SFPG for TETRA^[12]. Note that in TETRA E2EE, the keys are generated by a Key Management Centre (KMC) or a Key Management Facility (KMF), not by the communicating users.^[13]

Later, around 2014, the meaning of 'end-to-end encryption' started to evolve, requiring that not only the communication stays encrypted during transport, but also that the provider of the communication service is not able to decrypt the communications. This new meaning is now the widely accepted one.

Challenges[edit]

Man-in-the-middle attacks[edit]

End-to-end encryption ensures that data is transferred securely between endpoints. But, rather than try to break the encryption, an eavesdropper may impersonate a message recipient (during key exchange or by substituting his public key for the recipient's), so that messages are encrypted with a key known to the attacker. After decrypting the message, the snoop can then encrypt it with a key that they share with the actual recipient, or their public key in case of asymmetric systems, and send the message on again to avoid detection. This is known as a man-in-the-middle attack (MITM).^[1][14]

Authentication[edit]

Most end-to-end encryption protocols include some form of endpoint authentication specifically to prevent MITM attacks. For example, one could rely on certification authorities or a web of trust.^[15] An alternative technique is to generate cryptographic hashes (fingerprints) based on the communicating users’ public keys or shared secret keys. The parties compare their fingerprints using an outside (out-of-band) communication channel that guarantees integrity and authenticity of communication (but not necessarily secrecy), before starting their conversation. If the fingerprints match, there is in theory, no man in the middle.^[1]

When displayed for human inspection, fingerprints are usually encoded into hexadecimal strings. These strings are then formatted into groups of characters for readability. For example, a 128-bit MD5 fingerprint would be displayed as follows:

Some protocols display natural language representations of the hexadecimal blocks.^[16] As the approach consists of a one-to-one mapping between fingerprint blocks and words, there is no loss in entropy. The protocol may choose to display words in the user's native (system) language.^[16] This can, however, make cross-language comparisons prone to errors.^[17] In order to improve localization, some protocols have chosen to display fingerprints as base 10 strings instead of hexadecimal or natural language strings.^[18][17] Modern messaging applications can also display fingerprints as QR codes that users can scan off each other's devices.^[18]

Endpoint security[edit]

The end-to-end encryption paradigm does not directly address risks at the communications endpoints themselves. Each user's computer can still be hacked to steal his or her cryptographic key (to create a MITM attack) or simply read the recipients’ decrypted messages both in real time and from log files. Even the most perfectly encrypted communication pipe is only as secure as the mailbox on the other end.^[1] Major attempts to increase endpoint security have been to isolate key generation, storage and cryptographic operations to a smart card such as Google's Project Vault.^[19] However, since plaintext input and output are still visible to the host system, malware can monitor conversations in real time. A more robust approach is to isolate all sensitive data to a fully air gapped computer.^[20] PGP has been recommended by experts for this purpose:

Gsm Key Generation And Encryption Process 1

If I really had to trust my life to a piece of software, I would probably use something much less flashy — GnuPG, maybe, running on an isolated computer locked in a basement.

Gsm Key Generation And Encryption Process Free

However, as Bruce Schneier points out, Stuxnet developed by US and Israel successfully jumped air gap and reached Natanz nuclear plant's network in Iran.^[21] To deal with key exfiltration with malware, one approach is to split the Trusted Computing Base behind two unidirectionally connected computers that prevent either insertion of malware, or exfiltration of sensitive data with inserted malware.^[22]

Backdoors[edit]

A backdoor is usually a secret method of bypassing normal authentication or encryption in a computer system, a product, or an embedded device, etc.^[23] Companies may also willingly or unwillingly introduce backdoors to their software that help subvert key negotiation or bypass encryption altogether. In 2013, information leaked by Edward Snowden showed that Skype had a backdoor which allowed Microsoft to hand over their users' messages to the NSA despite the fact that those messages were officially end-to-end encrypted.^[24][25]

See also[edit]

• Comparison of instant messaging clients#Secure messengers – a table overview of instant messaging clients that offer end-to-end encryption
• Comparison of VoIP software#Secure VoIP software – a table overview of VoIP clients that offer end-to-end encryption
• Client-side encryption – the encryption of data before it is transmitted to a server

Gsm Key Generation And Encryption Processing

References[edit]

1. ^ ^abcd'Hacker Lexicon: What Is End-to-End Encryption?'. WIRED. 2014-11-25. Archived from the original on 23 December 2015. Retrieved 22 December 2015.
2. ^McLaughlin, Jenna (21 December 2015). 'Democratic Debate Spawns Fantasy Talk on Encryption'. The Intercept. Archived from the original on 23 December 2015.
3. ^Chris Alexander, Ian Avrum Goldberg (February 2007). Improved User Authentication in Off-The-Record Messaging(PDF). Proceedings of the 2007 ACM Workshop on Privacy in Electronic Society. pp. 41–47. doi:10.1145/1314333.1314340. ISBN9781595938831. Archived(PDF) from the original on 2016-02-27.
4. ^'End-to-End Encryption'. EFF Surveillance Self-Defense Guide. Electronic Frontier Foundation. Archived from the original on 5 March 2016. Retrieved 2 February 2016.
5. ^'How to: Use OTR for Windows'. EEF Surveillance Self-Defence Guide. Electronic Frontier Foundation. Archived from the original on 20 January 2016. Retrieved 2 February 2016.
6. ^Grauer, Yael. 'Mr. Robot Uses ProtonMail, But It Still Isn't Fully Secure'. WIRED. Archived from the original on 2017-03-09.
7. ^'Why Telegram's security flaws may put Iran's journalists at risk'. Committee to Protect Journalists. 31 May 2016. Archived from the original on 19 August 2016. Retrieved 23 September 2016.
8. ^Hackett, Robert (21 May 2016). 'Here's Why Privacy Savants Are Blasting Google Allo'. Fortune. Time Inc. Archived from the original on 10 September 2016. Retrieved 23 September 2016.
9. ^Baran, Paul (1964). 'IX. Security, Secrecy, and Tamper-Free Considerations. III. Some Fundamentals of Cryptography'. On Distributed Communications. RAND corporation.
10. ^Moldal, L.; Jorgensen, T. (11 February 2003). End to end encryption in GSM, DECT and satellite networks using NSK200. IET.
11. ^Murgatroyd, Brian (11 February 2003). End to end encryption in public safety TETRA networks. IET.
12. ^'New chair for the SFPG'. 2007.
13. ^Morquecho Martinez, Raul Alejandro (31 March 2016). Delivery of encryption keys in TETRA networks(PDF) (Master's Thesis). Aalto University.
14. ^Schneier, Bruce; Ferguson, Niels; Kohno, Tadayoshi (2010). Cryptography engineering : design principles and practical applications. Indianapolis, IN: Wiley Pub., inc. p. 183. ISBN978-0470474242.
15. ^'What is man-in-the-middle attack (MitM)? - Definition from WhatIs.com'. IoT Agenda. Archived from the original on 5 January 2016. Retrieved 7 January 2016.
16. ^ ^ab'pEp White Paper'(PDF). pEp Foundation Council. 18 July 2016. Archived(PDF) from the original on 1 October 2016. Retrieved 11 October 2016.
17. ^ ^abMarlinspike, Moxie (5 April 2016). 'WhatsApp's Signal Protocol integration is now complete'. Open Whisper Systems. Archived from the original on 10 October 2016. Retrieved 11 October 2016.
18. ^ ^abBudington, Bill (7 April 2016). 'WhatsApp Rolls Out End-To-End Encryption to its Over One Billion Users'. Deeplinks Blog. Electronic Frontier Foundation. Archived from the original on 12 September 2016. Retrieved 11 October 2016.
19. ^Julie Bort, Matt Weinberger 'Google's Project Vault is a tiny computer for sending secret messages'Archived 2017-08-08 at the Wayback Machine, Business Insider, NYC May 29, 2015
20. ^Whonix Wiki 'Air Gapped OpenPGP Key'Archived 2017-08-08 at the Wayback Machine
21. ^Bruce Schneier 'Air Gaps'Archived 2017-06-09 at the Wayback Machine, Schneier on Security, October 11, 2013
22. ^'maqp/tfc'. GitHub. Archived from the original on 31 March 2017. Retrieved 26 April 2018.
23. ^Eckersley, Peter; Portnoy, Erica (8 May 2017). 'Intel's Management Engine is a security hazard, and users need a way to disable it'. www.eff.org. Archived from the original on 6 March 2018. Retrieved 7 March 2018.
24. ^Goodin, Dan (20 May 2013). 'Think your Skype messages get end-to-end encryption? Think again'. Ars Technica. Archived from the original on 22 December 2015.
25. ^Greenwald, Glenn; MacAskill, Ewen; Poitras, Laura; Ackerman, Spencer; Rushe, Dominic (12 July 2013). 'Microsoft handed the NSA access to encrypted messages'. the Guardian. Archived from the original on 19 November 2015.

Further reading[edit]

• Ermoshina, Ksenia; Musiani, Francesca; Halpin, Harry (September 2016). 'End-to-End Encrypted Messaging Protocols: An Overview'(PDF). In Bagnoli, Franco; et al. (eds.). Internet Science. INSCI 2016. Florence, Italy: Springer. pp. 244–254. doi:10.1007/978-3-319-45982-0_22. ISBN978-3-319-45982-0.