I vincitori del Premio Tesi

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Titolo della tesi

“Automatic differential cryptanalysis of the SPECK block cipher with Monte Carlo Tree Search”

Relatore

Basile Cataldo (DAUIN), Bazzanella Danilo (DISMA)

Abstract

Nowadays, cryptography is one of the main building blocks in computer science, as it contributes to digital data security in the broadest sense, both when stored and when exchanged. Block ciphers play an important role in this scenario, as they represent some of the functions used to achieve cryptographic security. Differential cryptanalysis is a powerful tool to assess the security and robustness of ciphers and hash functions. This technique, which usually takes the form of a chosen plaintext attack, aims to analyse the multiple rounds in a block cipher. In practice, its purpose is to find sequences of perturbations, called differences, from the input of the cipher and up to the largest possible number of rounds so that the total propagation probability is as high as possible. When a good sequence (also called differential characteristic) is found, the attack is considered successful, and in some cases it can allow a key recovery attack, in which the secret key used with the cipher is discovered. The work described in this Thesis regards the automation of the search for differential characteristics in block ciphers. The case study focuses on the SPECK family of ciphers. The objective is to ease the security assessment of block ciphers by developing a tool capable of finding good sequences of differences in an automated way, with a very small knowledge of the target cipher and with no human interaction. The tool is based on a variant of the Monte-Carlo Tree Search (MCTS) called Single Player MCTS. Monte-Carlo Tree Search is a well-known algorithm in the context of board games such as Chess of Go because of its strength when the number of solutions is so high that a complete search is unfeasible, as is the case in cryptanalysis, but it is almost unexplored in this field. The research started from a survey of the works present in literature, which led to the discovery of precious heuristics that improve the performance of the MCTS algorithm. Then, the implementation phase has taken place, from the code for the precomputation of data needed to the algorithm, to the algorithm itself, the collection of statistics and the validation of the outcome. During this phase, several heuristics collected from previous works were gradually added to face the limitations that arose, and each addition contributed positively to the global performance of the algorithm. At last, a comparison between the new tool and the existing ones is performed: although graph-based searches are the natural competitor of the Monte-Carlo Tree Search, due to their internal behaviour, also solver-based ones are taken into account. The results are promising as the search is significantly faster than the state-of-the-art works for the smallest versions of SPECK, while non-optimal but still good results are obtained for the bigger version. Moreover, additional optimizations can be introduced, leaving room to further improvements in the already good results.

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Titolo della tesi

“Assessment of the Blocking Cards Effectiveness in Protecting Mifare Classic Smart Card”

Relatore

Alessio Meneghetti, Edoardo Persichetti, Michele Battagliola

Abstract

Smart Cards are physical cards that can connect to a reader either by direct physical contact or through a short-range wireless connectivity standard such as Radio-Frequency IDentification (RFID) or Near Field Communication (NFC). In particular, due to their speed and convenience, contactless smart cards are rapidly becoming one of the most widely used technologies with major deployments worldwide in applications such as micropayment, physical and logical access control, corporate IDs, and automatic fare collection. The MIFARE Classic produced by NXP Semiconductors is currently one of the most used contactless smart cards, with more than 5 billion cards sold worldwide. Due to their use cases, smart cards are increasingly being targeted by cyber criminals who want to retrieve users’ sensitive information or any profitable data. As a consequence, several countermeasures have been designed, such as blocking cards, which currently represent one of the most common and affordable defense mechanisms. They are usually kept in a pocket or wallet to block potential attacks by emitting a noisy jamming signal or physically shielding the smart card. This work introduces an attack against the MIFARE Classic smart card that can be carried out even in the presence of a blocking card, employing a Software Defined Radio (SDR) to capture and analyze the raw signal of a communication between the card and the reader. Then, we analyze the effectiveness of five different blocking cards by comparing their performance in protecting a MIFARE Classic from the introduced attack. Finally, by analyzing them individually, we will show how blocking cards that add noise signals at multiple fixed frequencies offer the highest possible level of protection.

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Titolo della tesi

“Reversing, Analyzing, and Attacking Xiaomi’s Electric Scooter Ecosystem”

Relatore

Abstract

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Titolo della tesi

“Lightweight Real-Time Ransomware Detection with Native OS Assistance via ETW”

Relatore

Prof. Daniele Cono D’Elia

Abstract

I ransomware sono una classe di malware che rende inaccessibili i dati dei computer infettati chiedendo il pagamento di un riscatto per ripristinarli. Quando la vittima è un’organizzazione, gli attaccanti spesso colpiscono simultaneamente l’intera infrastruttura per paralizzarla. Queste minacce hanno costretto i vendor di sistemi di sicurezza a cambiare approccio verso detection e reaction: non basta più riconoscere e rimuovere un’infezione, ma serve fermarla prima che sia troppo tardi; ciò rende diversi sistemi attuali inefficaci verso il ransomware. Questa tesi propone una soluzione alternativa ed originale per ransomware detection su ambienti Windows. Sviluppata in un tirocinio in Leonardo S.p.A., è progettata per l’impiego in scenari reali accanto a sistemi di monitoraggio real-time esistenti, quali EDR, senza alterare il funzionamento dell’infrastruttura sottostante. La soluzione si avvale di Event Tracing for Windows (ETW): questa funzionalità nativa del kernel di Windows risulta essere molto leggera in overhead ed offre elevata compatibilità con il software esistente. Inoltre, evita le limitazioni implementative di userland API hooks (aggirabili facilmente con tecniche note) e dei kernel drivers (spesso complessi da sviluppare e proni a generare un alto carico CPU). La soluzione si basa su euristiche di detection nate da un’approfondita attività di reverse engineering dei tratti comportamentali di molteplici varianti di ransomware appartenenti a famiglie diverse. La tesi presenta in modo esaustivo alcune di tali varianti e analizza nel dettaglio gli eventi valutati come riconducibili con alta probabilità ad attacchi ransomware. La soluzione si compone di quattro moduli cooperanti e specializzati sulle caratteristiche degli eventi in questione. Rispettivamente, i moduli operano attraverso: (i) intercettare l’utilizzo illegittimo di strumenti di amministrazione; (ii) identificare pattern di accesso e modifica dei file che sono riconducibili a ransomware; (iii) individuare correlazioni insolite tra specifici eventi (es. create/delete); (iv) sfruttare il pattern di creazione delle note di riscatto che è caratteristico di alcune famiglie di ransomware. Monitorare caratteristiche comportamentali che sono generali tra i ransomware consente una detection precisa ed agnostica, senza dover far ricorso a signature ottenibili analizzando varianti già note di una stessa minaccia. Il prototipo implementato è:?- Automatizzato, leggero, real-time: richiede moderate risorse computazionali per analizzare gli enormi flussi ETW; esegue l’analisi dinamica in tempo reale di tutti i processi in esecuzione; termina in autonomia quelli sospetti. - Accurato, veloce, robusto: nella sperimentazione, dimostra di rilevare velocemente ransomware appartenenti a famiglie e varianti non note al momento dello sviluppo. - Proattivo: può intercettare sul nascere (ossia senza corruzione di alcun file) alcune famiglie di ransomware che fanno uso di specifici comandi da amministratore. - Personalizzabile: il responsabile della sicurezza di perimetro può tarare moduli e filtri sugli eventi secondo proprie policy di sicurezza interna e strategie di rischio cyber. Per la valutazione sperimentale, si è costruito un ambiente di test rappresentativo di un ambiente di un utente standard secondo le best practices dell’area, con test automatizzati per avere risultati scientificamente riproducibili. Per evitare overfitting delle euristiche, si è diversificato il più possibile il dataset di test, analizzando 111 campioni provenienti da 25 famiglie di ransomware diverse, per poi verificare possibili falsi positivi da programmi legittimi (es., che fanno frequente ricorso a cifratura e compressione). Il prototipo mostra un tasso di detection pari al 98,2% senza falsi positivi, con un numero di file compromessi spesso compreso tra zero e le poche decine (prima che il sample venga rilevato e terminato), con consumo di CPU minore dell’1% e l’utilizzo di RAM nell’ordine di poche decine di MB.

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Titolo della tesi

“FairDrop: a Confidential Fair Exchange Protocol for Media Workers”

Relatore

Prof. Mauro Conti

Abstract

In recent years, the asymmetry between open societies and regimes that control their media has increased, leading to the number of murdered journalists more than doubling worldwide. Even in countries in which freedom of the press is publicly recognized, the number of journalists jailed, assaulted, or criminally charged is relevant and growing. These attacks on media workers usually want to limit or control information regarding critical topics. In this context, the necessity of a system that allows reporters to publish their works without risking their own life is evident. Some systems to share information with newspapers while keeping the source anonymous exist. An example is SecureDrop, developed and maintained by the Freedom of the Press Foundation, and widely adopted by all major international newspapers. What limits them from extensively using this type of system is the lack of credibility in the information exchanged, which represents the main problem for the publisher’s reputation. In this thesis, we present FairDrop, a system that allows the exchange of information between two untrusted parties and proposes a tradeoff between the anonymity of the source and the credibility of the information exchanged. We present a fair exchange protocol based on blockchain that allows sharing of a digital good fairly and confidentially. We also define the guidelines for a system based on ring signatures to measure the credibility of the exchanged information. All our design decisions are made taking into account the requirements of a journalist-newspaper communication, and the guidelines for anonymous sources applied by major newspapers around the world. We test the system in a real-world blockchain testnet, considering multi-seller and buyer situations, and introducing economic incentives for sources to use the system.