FHEVM

• Name: FHEVM
• URL: https://github.com/zama-ai/fhevm
• Category: confidential smart-contract framework / encrypted-state execution middleware / FHE coprocessor-and-gateway stack
• Tags: ethereum-ecosystem
• Summary: FHEVM is the core framework inside the broader Zama Confidential Blockchain Protocol, and it is worth cataloging separately because it exposes a cleaner lower-layer control surface than the umbrella brand alone. The current docs and repository make FHEVM legible as a split system: Solidity contracts stay onchain and operate on encrypted handles symbolically, while offchain coprocessors perform the actual FHE work, gateway contracts mediate verification and decryption flows, and TKMS/KMS components manage keys and reencryption. That makes FHEVM a useful comparison class for Fhenix and Oasis Sapphire because the important question is not just can this EVM app be private? but where confidentiality policy, computation, key management, and developer ergonomics actually sit.
• What it does:
  • Extends Solidity with encrypted types like ebool, euint8...euint256, eint8...eint256, and eaddress, plus encrypted arithmetic, comparison, logic, branching, and random-value generation
  • Lets contracts accept externally encrypted inputs with attestations, convert them into onchain handles, and manage ciphertext permissions through ACL-style allow, allowTransient, and decryption authorization flows
  • Uses symbolic execution on the host chain so contracts manipulate encrypted handles onchain while offchain coprocessors perform the underlying FHE computations asynchronously
  • Surrounds the Solidity library with host contracts, gateway contracts, coprocessor services, and TKMS/KMS components that handle ciphertext commitments, decryption / reencryption, validator-set updates, and key material publication
  • Gives developers a fairly direct plain Solidity -> confidential Solidity migration path through official Hardhat templates, guides, example contracts, and fhevmjs
  • Targets confidential transfers, tokenization, blind auctions, confidential voting, games, and encrypted identity / attestation-style applications without requiring a separate privacy chain UX
• Key claims:
  • The official README calls FHEVM the core framework of the Zama Confidential Blockchain Protocol and says it enables confidential smart contracts on EVM-compatible blockchains through fully homomorphic encryption rather than TEEs or a separate privacy-only L1/L2
  • The repo and docs describe a distinct architectural split: host-chain contracts do symbolic execution and emit events, coprocessors perform FHE computation offchain, and gateway / TKMS layers handle input verification, decryption, reencryption, and validator-set or key-management-facing updates
  • The library docs emphasize that encrypted values are represented onchain as handles to offchain ciphertext state, which is analytically important because confidentiality lives in a handle-plus-coprocessor model rather than in ordinary plaintext EVM execution
  • The quick-start and transformation guides show a practical migration path where developers start from a normal Solidity contract, replace sensitive values with encrypted types, use FHE.fromExternal / FHE.select / encrypted operators, and then handle asynchronous decryption plus proof verification
  • The docs present FHEVM as composable with existing EVM workflows and existing dApps, which makes it a stronger comparison point for middleware-style confidential execution than projects that require a wholly separate chain environment
  • The README FAQ also matters as a governance/adoption signal: Zama distributes the code under BSD-3-Clause-Clear for development, research, prototyping, and experimentation, while commercial users need a separate patent license
• Whitepaper: Official whitepaper saved locally as ../whitepapers/zama-fhevm-whitepaper.pdf. Additional primary-source notes for this pass are saved in ../whitepapers/fhevm-primary-sources-2026-05-14.md.
• Sources:
  • https://github.com/zama-ai/fhevm
  • https://raw.githubusercontent.com/zama-ai/fhevm/main/README.md
  • https://docs.zama.org/protocol/zama-protocol-litepaper
  • https://docs.zama.org/protocol/protocol/overview/library
  • https://docs.zama.org/protocol/protocol/overview/library.md?ask=What%20off-chain%20components%20does%20the%20FHEVM%20library%20interact%20with%2C%20and%20what%20control%20surfaces%20do%20they%20handle%3F
  • https://docs.zama.org/protocol/solidity-guides/getting-started/quick-start-tutorial.md?ask=What%20developer-facing%20capabilities%20and%20workflow%20does%20the%20quick-start%20show%20for%20building%20a%20confidential%20Solidity%20contract%3F
  • https://docs.zama.org/protocol/protocol-guides.md?ask=Summarize%20the%20official%20protocol-side%20components%20and%20apps%20that%20surround%20FHEVM%2C%20including%20gateway%2C%20host%20contracts%2C%20coprocessor%2C%20KMS%2C%20and%20user-facing%20apps.
  • https://raw.githubusercontent.com/zama-ai/fhevm/main/fhevm-whitepaper.pdf

Internal linkages

• Keep the split clean: zama is the umbrella entity note; FHEVM is the lower-layer framework note.

• Best confidential-EVM comparison points: fhenix and oasis-sapphire.

• Last reviewed: 2026-06-14 UTC