Hex Conventions

Root14 uses two hex formats depending on context: 0x-prefixed for human-readable wallet data, and raw (no prefix) for Soroban contract arguments.

Format Table

Context	Prefix	Length	Example
wallet::fr_to_hex	0x	66 chars	0x00ab12...ef
wallet::hex_to_fr (input)	optional 0x	any	0xab, ab
wallet::fr_to_raw_hex	none	64 chars	00ab12...ef
merkle module (output)	none	64 chars	00ab12...ef
serialize::serialize_fr	none	64 chars	00ab12...ef
serialize::serialize_g1	none	192 chars	aabb...
serialize::serialize_g2	none	384 chars	aabb...
Soroban contract args	none	varies	strip 0x before passing
Indexer API responses	0x	66 chars	0x1a2b...

Why Two Formats

• 0x-prefixed (fr_to_hex): Used in the wallet JSON file and user-facing output. Familiar to developers from Ethereum/EVM conventions. 66 characters total: 2 for 0x + 64 hex digits representing 32 bytes.

• No prefix (fr_to_raw_hex, serialize_fr): Used for Soroban contract arguments. Soroban's BytesN<32>::from_hex expects raw hex without a prefix. The serialize module also outputs raw hex since its output is consumed directly by contract calls.

Converting Between Formats

use r14_sdk::wallet::{fr_to_hex, fr_to_raw_hex, hex_to_fr, strip_0x};

let fr = hex_to_fr("0x1a2b3c")?;      // accepts 0x prefix
let fr = hex_to_fr("1a2b3c")?;         // also works without

let with_prefix = fr_to_hex(&fr);       // "0x001a2b3c...00" (66 chars)
let without_prefix = fr_to_raw_hex(&fr); // "001a2b3c...00" (64 chars)

// Strip prefix from existing string
let raw = strip_0x("0xdeadbeef");        // "deadbeef"
let raw = strip_0x("deadbeef");          // "deadbeef" (no-op)

Gotchas

Always strip 0x before passing to Soroban. The invoke_contract function passes values directly to the Stellar CLI. Soroban contract functions expect raw hex bytes. Passing 0x-prefixed values will cause decoding errors on-chain.

// Correct
let cm_hex = fr_to_raw_hex(&cm);
invoke_contract(&contract, "testnet", &secret, "deposit", &[("cm", &cm_hex)]).await?;

// Also correct
let cm_hex = strip_0x(&fr_to_hex(&cm));

// Wrong - will fail on-chain
let cm_hex = fr_to_hex(&cm); // has 0x prefix

hex_to_fr zero-pads short inputs. If you pass a short hex string like "01", it is left-padded with zeros to 32 bytes. This means hex_to_fr("01") produces Fr::from(1u64).

Serialized public inputs use serialize_fr. The output from serialize_proof_for_soroban returns public inputs as raw hex (no prefix, 64 chars). These come from serialize_fr, which reverses the arkworks LE byte order to BE for Soroban compatibility.

Indexer returns 0x-prefixed hex. The indexer's API responses (root, siblings, leaves) all use 0x-prefixed format. Strip before passing to Soroban:

let siblings: Vec<Fr> = response.siblings.iter()
    .map(|s| hex_to_fr(s))  // hex_to_fr handles 0x prefix automatically
    .collect::<Result<_>>()?;

Byte Sizes Reference

Type	Bytes	Hex chars (raw)	Hex chars (0x)
Fr (scalar)	32	64	66
G1 (uncompressed)	96	192	194
G2 (uncompressed)	192	384	386