fhenix-trivial-encryption

---
name: fhenix-trivial-encryption
description: Convert plaintext to encrypted types on-chain with FHE.asEuintXX/asEbool/asEaddress (+ optional securityZone), and understand the critical caveat — trivially-encrypted values are NOT confidential. Covers the full cross-cast matrix and the wrap*/asE* renaming.
license: MIT
---

# Fhenix Trivial Encryption

## Overview
**Trivial encryption** converts a plaintext Solidity value into an encrypted type so it can interact with real ciphertexts, using the `FHE.asE…` family:
```solidity
uint16 number = 2;
euint16 enc = FHE.asEuint16(number);
ebool   flag = FHE.asEbool(true);
eaddress a   = FHE.asEaddress(0x1234...7890);
euint32  z   = FHE.asEuint32(50000, 1);   // optional securityZone
```

## ⚠️ Trivially-encrypted values are NOT confidential
The plaintext was public, so the result stays public — anyone watching the chain knows the value (it just has an encrypted *type*). Combining two trivially-encrypted values yields another non-confidential value (the observer can replay the math). **Confidentiality only comes from `InEuintXX` inputs encrypted client-side.** Treat any `FHE.asE…(literal)` result as public.

```solidity
function calc(InEuint16 calldata input) public {
    euint16 number5  = FHE.add(FHE.asEuint16(2), FHE.asEuint16(3)); // public (=5)
    euint16 encInput = FHE.asEuint16(input);                        // confidential
    euint16 encMul   = FHE.mul(encInput, number5);                 // confidential
    // observer knows the structure, not the secret value
}
```

## Two meanings of `FHE.asEuintXX(...)`
- **From plaintext** (trivial encryption) — `FHE.asEuint32(50000)`.
- **From an `InE*` input struct** — `FHE.asEuint32(inEuint32)` (this *is* confidential; see `fhenix-encrypted-inputs`).

## Cross-casting between encrypted types
The full matrix is supported, e.g. `FHE.asEbool(euintN)`, `FHE.asEuint8(euint128)`, `FHE.asEaddress(euint128)`, etc. Narrowing/widening casts each emit an FHE op.

## Handle-wrapping rename (cofhe-contracts ≥ 0.1.3)
Wrapping a raw `bytes32` handle into a typed value moved from `FHE.asE*(bytes32)` to dedicated `FHE.wrap*` functions (`wrapEbool`, `wrapEuint8…128`, `wrapEaddress`) to remove an overload ambiguity with `asEuint*(0)`. `FHE.unwrap(x)` extracts the `bytes32` handle. If upgrading from ≤0.1.2, rewrite `FHE.asE*(<bytes32>)` call sites as `FHE.wrap*`.

## Source docs
- [`fhe-library/core-concepts/trivial-encryption.mdx`](../fhenix-docs/fhe-library/core-concepts/trivial-encryption.mdx)
- [`fhe-library/reference/fhe-sol/type-conversion.mdx`](../fhenix-docs/fhe-library/reference/fhe-sol/type-conversion.mdx) · [`utility.mdx`](../fhenix-docs/fhe-library/reference/fhe-sol/utility.mdx)

## AI Agent Prompt
> "Explain why a trivially-encrypted constant (e.g. a counter delta of 1) is safe to make public but a user balance must come from an `InEuintXX`. Then show a function mixing a public `FHE.asEuint32(1)` delta with a confidential input."