Charles Guillemet

Charles Guillemet is Chief Technology Officer of Ledger, the French cryptocurrency security company best known for its hardware wallets. Ledger announced his appointment to the role on 5 December 2019, stating that he would keep his oversight of the company's security operations. He had joined Ledger in 2017 as Chief Security Officer and founded the Ledger Donjon, the company's in-house security evaluation lab, that year. Ledger credits him with establishing its security department and with obtaining independent security certifications for the Ledger Nano S and Ledger Nano X.

Before Ledger, Guillemet spent about ten years in cryptography and hardware security. He began his career at Tiempo, a secure-industry start-up, where he designed the security of EAL5+ secure integrated circuits, and then worked as technical manager at a Common Criteria accredited security evaluation facility at the CEA. He holds a Master of Science in Cryptography and Security from the ENSIMAG engineering school, where he graduated as valedictorian and later taught smart-card security.

The Donjon evaluates the security of Ledger's own devices and those of other manufacturers, and discloses what it finds responsibly. Its published disclosures include a side-channel attack on the PIN verification of the Trezor One (2018), weak entropy in the Trust Wallet browser extension (2022) and a brute-force weakness in Tangem cards (2025). In September 2026 Ledger described Cerberus, a team of six specialised AI agents built by the Donjon to find, verify and fix security flaws, and reported that four of its findings in third-party software had been assigned CVEs.

In an April 2026 interview with CoinDesk, Guillemet argued that AI is making it far cheaper and easier to find and exploit vulnerabilities, and that a dedicated device not exposed to the internet is more secure by design.

Guillemet spoke at Proof of Talk Paris 2026 on the Hecto Main Stage on 3 June 2026, the summit's second day, as a panellist on "DeFi Under Attack: Securing Onchain Finance and the Machine Economy", alongside Kostas Chalkias, Rodrigo Coelho and Jason Jiang. Nikola Stojanow moderated the session.