Charles Guillemet

Who they are

Charles Guillemet is CTO at Ledger — valedictorian MSc in Cryptography from ENSIMAG and founder of Ledger Donjon, the company's internal security research team.

Person

Charles joined Ledger in December 2017, when the company was still establishing itself as a hardware wallet maker — he came in as CSO and founded Ledger Donjon, an internal security research team dedicated to attacking Ledger's own products before adversaries can. His academic foundation is deep: valedictorian MSc in Cryptography and Security at ENSIMAG, plus a Master 2 in Security, Cryptology and Coding of Information Systems from Université Joseph Fourier. Before Ledger he worked at CEA-LETI ITSEF, France's national applied-research lab, as a Cryptosystems Design Expert and Technical Manager — serious government-adjacent security work — and also held a lecturing role at ENSIMAG. He passed through Tiempo S.A.S. along the way, a semiconductor security IP company, rounding out his hardware-focused pedigree. He was promoted to CTO after his CSO tenure, a move that expanded his scope from pure security to all of Ledger's technical direction. He writes on Medium about cryptography, blockchain security, and hardware security, and speaks regularly at ETH Denver, BTC Prague, Black Hat MEA, Blockworks, and Proof of Talk — always anchored on self-custody, secure enclaves, and the technical realities of keeping crypto safe.

Company

Ledger's most recent strategic moment is a paused U.S. IPO: in May 2026, the company shelved plans for a listing that had targeted a valuation over $4 billion, citing volatile market conditions and weak investor appetite for crypto listings, and is now evaluating private capital raises instead. That same quarter, Ledger reported record-breaking revenue in Q1 2026, driven by surging demand for self-custody solutions amid geopolitical instability — the company is choosing to stay private to maintain operational flexibility despite strong fundamentals. On the product side, Ledger released a 2026 AI security roadmap in early 2026, introducing hardware-anchored security for AI agents with phased features including Agent Identity, Agent Intents and Policies, and Proof of Human — a pointed move into securing the emerging agent economy. The company also introduced enterprise-grade on-premises hardware security solutions and evolving tokenized investment strategies to serve institutional crypto participants. March 2026 also brought a leadership addition: John Andrews, formerly of Circle, joined as CFO alongside the opening of a New York office focused on institutional business and the Ledger Enterprise platform.

Market

Ledger claims roughly 25% of the retail hardware wallet market and secures approximately 20% of the world's cryptocurrency assets, operating across more than 200 countries — a dominant position in self-custody infrastructure. Its main competitors are CertiK, MetaMask, and Casa, though the competitive set is broadening as Ledger moves upmarket into institutional and enterprise security. Regulatory headwinds — including the U.S. CLARITY Act, Hong Kong stablecoin rules, and cross-jurisdictional AML and GDPR fragmentation — continue to shape the pace and geography of crypto adoption, while the U.S. market is gradually stabilizing with moves like SEC tokenized securities approval.

Network

Guillemet's closest named collaborators at Ledger are CEO Pascal Gauthier, to whom he reports as a peer executive, and Arnaud Prigent, Head of Product, with whom he works directly on product and security direction. Quentin Ricomard sits alongside him as CFO in the leadership team, now joined by incoming CFO John Andrews focused on U.S. institutional expansion.

Pascal Gauthier· CEO, Ledger
Arnaud Prigent· Head of Product, Ledger
Quentin Ricomard· CFO, Ledger
John Andrews· Incoming CFO / U.S. expansion lead, Ledger (formerly Circle)

How they likely show up

Long tenure at Ledger since December 2017 — CSO to CTO over a multi-year arc — signals he thinks in sustained technical bets, not short cycles.
Founded Ledger Donjon (an internal red team) from scratch → he builds institutions around problems rather than waiting for someone else to solve them.
Career path from CEA-LETI ITSEF (national applied research) through semiconductor IP (Tiempo S.A.S.) to product CTO → he bridges deep academic/government security work and commercial product reality, unusual for a CTO.
Active speaker at ETH Denver, BTC Prague, Black Hat MEA, and Blockworks → comfortable across both crypto-native and professional security audiences; likely adapts his framing depending on who's in the room.
Writes on Medium on cryptography and hardware security, and lectured at ENSIMAG → teaching instinct, probably explains technical concepts clearly and appreciates when others come prepared.
Valedictorian at ENSIMAG → high standards orientation; likely direct about technical correctness and skeptical of hand-wavy security claims.

Conversation tips

→ Come in with a specific technical question about hardware security or secure enclaves — vague crypto enthusiasm won't engage him the way a precise technical framing will.
→ Reference Ledger Donjon specifically — he founded it and it reflects his philosophy that you find your own bugs first; it's a point of genuine pride.
→ His AI security roadmap (Agent Identity, Agent Intents and Policies, Proof of Human) is a live bet — asking about the threat model behind it will show you've done the work.
→ He lectures and publishes — treat the conversation as a peer exchange, not a pitch; he'll engage more if you bring your own view to test against his.
→ Don't conflate 'hardware security' with 'crypto wallet product' — his background goes well beyond consumer hardware to cryptosystem design and formal security research.

Toolbox

Openers

Open on Ledger Donjon — he founded the internal red team in 2017, the same year he joined, which means his first instinct on arrival was to build a team whose job is to break the product. That's a specific philosophy worth unpacking.
Reference his 2026 AI security roadmap — Ledger released a phased plan to provide hardware-anchored security for AI agents, covering Agent Identity, Agent Intents and Policies, and Proof of Human. It's a pointed technical bet that the agent economy inherits the same trust problems as crypto keys.
Lead with the ETH Denver or Black Hat MEA appearances — he speaks at both the crypto-native and professional security circuit, which is an unusual double. Ask how his framing of self-custody changes between those two audiences.

Discovery questions

When you founded Ledger Donjon, what was the first serious vulnerability the team found — and did it change how the hardware team was structured afterward?
The 2026 AI security roadmap introduces 'Proof of Human' as a feature — what's the threat model there, and does hardware attestation actually solve it or just raise the cost of attack?
You moved from CSO to CTO — how much of your technical agenda as CTO is still security-first versus areas where you've had to develop genuinely new instincts?

Avoid

Don't make soft claims about 'the importance of security in crypto' — he has a formal cryptography background, founded a red team, and speaks at Black Hat; he'll expect precision, not platitudes.

Make it yours