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1. Biased Nonce Sense: Lattice Attacks Against Weak ECDSA Signatures in Cryptocurrencies

   https://doi.org/10.1007/978-3-030-32101-7_1  

   Breitner, Joachim ; Heninger, Nadia ( January 2019 , FC 2019: Financial Cryptography and Data Security)

   In this paper, we compute hundreds of Bitcoin private keys and dozens of Ethereum, Ripple, SSH, and HTTPS private keys by carrying out cryptanalytic attacks against digital signatures contained in public blockchains and Internet-wide scans. The ECDSA signature algorithm requires the generation of a per-message secret nonce. If this nonce is not generated uniformly at random, an attacker can potentially exploit this bias to compute the long-term signing key. We use a lattice-based algorithm for solving the hidden number problem to efficiently compute private ECDSA keys that were used with biased signature nonces due to multiple apparent implementation vulnerabilities. 

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2. TPM-Fail:TPM meets Timing and Lattice Attacks

   Moghimi, Daniel ; Sunar, Berk ; Eisenbarth, Thomas ; Heninger, Nadia ( January 2020 , 29th USENIX Security Symposium (USENIX Security 20))

   null (Ed.)

   Trusted Platform Module (TPM) serves as a hardwarebased root of trust that protects cryptographic keys from privileged system and physical adversaries. In this work, we perform a black-box timing analysis of TPM 2.0 devices deployed on commodity computers. Our analysis reveals that some of these devices feature secret-dependent execution times during signature generation based on elliptic curves. In particular, we discovered timing leakage on an Intel firmwarebased TPM as well as a hardware TPM. We show how this information allows an attacker to apply lattice techniques to recover 256-bit private keys for ECDSA and ECSchnorr signatures. On Intel fTPM, our key recovery succeeds after about 1,300 observations and in less than two minutes. Similarly, we extract the private ECDSA key from a hardware TPM manufactured by STMicroelectronics, which is certified at Common Criteria (CC) EAL 4+, after fewer than 40,000 observations. We further highlight the impact of these vulnerabilities by demonstrating a remote attack against a StrongSwan IPsec VPN that uses a TPM to generate the digital signatures for authentication. In this attack, the remote client recovers the server’s private authentication key by timing only 45,000 authentication handshakes via a network connection. The vulnerabilities we have uncovered emphasize the difficulty of correctly implementing known constant-time techniques, and show the importance of evolutionary testing and transparent evaluation of cryptographic implementations. Even certified devices that claim resistance against attacks require additional scrutiny by the community and industry, as we learn more about these attacks. 

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3. TPM-FAIL: TPM meets Timing and Lattice Attacks

   Moghimi, Daniel ; Sunar, Berk ; Eisenbarth, Thomas ; Heninger, Nadia ( January 2020 , Proceedings of the 29th USENIX Security Symposium)

   null (Ed.)

   Trusted Platform Module (TPM) serves as a hardware based root of trust that protects cryptographic keys from privileged system and physical adversaries. In this work, we perform a black-box timing analysis of TPM 2.0 devices deployed on commodity computers. Our analysis reveals that some of these devices feature secret-dependent execution times during signature generation based on elliptic curves. In particular, we discovered timing leakage on an Intel firmware based TPM as well as a hardware TPM. We show how this information allows an attacker to apply lattice techniques to recover 256-bit private keys for ECDSA and ECSchnorr signatures. On Intel fTPM, our key recovery succeeds after about 1,300 observations and in less than two minutes. Similarly, we extract the private ECDSA key from a hardware TPM manufactured by STMicroelectronics, which is certified at Common Criteria (CC) EAL 4+, after fewer than 40,000 observations. We further highlight the impact of these vulnerabilities by demonstrating a remote attack against a StrongSwan IPsec VPN that uses a TPM to generate the digital signatures for authentication. In this attack, the remote client recovers the server’s private authentication key by timing only 45,000 authentication handshakes via a network connection. The vulnerabilities we have uncovered emphasize the difficulty of correctly implementing known constant-time techniques, and show the importance of evolutionary testing and transparent evaluation of cryptographic implementations. Even certified devices that claim resistance against attacks require additional scrutiny by the community and industry, as we learn more about these attacks. 

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4. New Secure Approach to Backup Cryptocurrency Wallets

   https://doi.org/10.1109/GLOBECOM38437.2019.9014007  

   Rezaeighaleh, Hossein ; Zou, Cliff C. ( December 2019 , 2019 IEEE Global Communications Conference (GLOBECOM))

   Bitcoin and other cryptocurrencies have become popular and motivate more hackers to steal digital funds. Users protect their private keys using crypto wallets to keep their funds safe from hackers. While the most secure option is hardware wallet, it suffers from lack of a secure and convenient backup and recovery process. Almost all existing wallets use mnemonics to back up the private keys, and a user must write down these words on a piece of paper. This approach is not only inconvenient but also problematic since the paper could be lost or stolen, resulting in a hacker recovering the keys. In this paper, we propose a new digital scheme to securely back up a hardware wallet relying on the side-channel human visual verification enabled by display screen on a hardware wallet. Using this method, we transfer the root of private keys from one hardware wallet to another wallet securely even via an untrusted terminal, such as a smartphone. At the end of this process, the user has two hardware wallets with the same private keys while she may use one of them as the main wallet and another one as a backup wallet. 

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5. Multilayered Defense-in-Depth Architecture for Cryptocurrency Wallet

   https://doi.org/10.1109/ICCC51575.2020.9345013  

   Rezaeighaleh, Hossein ; Zou, Cliff C. ( December 2020 , 2020 IEEE 6th International Conference on Computer and Communications (ICCC))

   null (Ed.)

   A significant challenge in blockchain and cryptocurrencies is protecting private keys from potential hackers because nobody can rollback a transaction made with a stolen key once the blockchain network confirms the transaction. The technical solution to protect private keys is cryptocurrency wallets, a piece of software, hardware, or a combination of them to manage the keys. In this paper, we propose a multilayered architecture for cryptocurrency wallets based on a Defense-in-Depth strategy to protect private keys with a balance between convenience and security. The user protects the private keys in three restricted layers with different protection mechanisms. So, a single breach cannot threaten the entire fund, and it saves time for the user to respond. We implement a proof-of-concept of our proposed architecture on both a smart card hardware wallet and an Android smartphone wallet with no performance penalty. Furthermore, we analyze the security of our proposed architecture with two adversary models. 

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