PriFi.info

Firo

A proof-of-work cryptocurrency, formerly Zcoin, whose Lelantus Spark protocol hides the sender, receiver and amount of Spark transactions, alongside transparent addresses that work as in Bitcoin.

LivePrivacy coin

As of 23 October 2026 the mainnet ran Lelantus Spark; the v0.14.18.0 hard fork, set for block 1,371,000 on about 4 September 2026, was to restore multi-input Spark spends after the forgery flaw disclosed in August 2026, and releases v0.14.18.1 and v0.14.18.2 followed on 26 September and 16 October with wallet and interface changes.

Market cap
$15.9MDefiLlama, 28 Oct 2026
Launched
28 Sep 2016
Token
FIRO
Chains
Firo

Checked on 23 Oct 2026. Information only, not investment advice.

How it works

Firo is a cryptocurrency with its own blockchain, launched on 28 September 2016 as Zcoin, built on the Zerocoin protocol, and renamed Firo on 30 November 2020 on the same chain. Miners add blocks with proof-of-work, since 26 October 2021 on FiroPoW, a variant of ProgPoW, and since June 2022 about every two and a half minutes. Masternodes, which since September 2024 receive 70% of each block reward, run InstantSend and ChainLocks, in which quorums of masternodes sign blocks so that they cannot be reorganised away; ChainLocks were brought forward after a 51% attack in January 2021.

Privacy is optional. Firo keeps transparent addresses that work as in Bitcoin, beside private Spark addresses, which since Lelantus Spark activated at block 819,300 on 18 January 2024 have been the default way to send and receive FIRO in the official wallets. Spark, designed by Aram Jivanyan of Firo with Aaron Feickert of Cypher Stack, hides the sender, the receiver and the amount of a Spark transaction. A spend proves with a one-out-of-many zero-knowledge proof that the coin it consumes is one of a set of earlier Spark coins, without saying which, and Firo's code sets the largest Spark anonymity set at 32,000 coins. Amounts are hidden in Pedersen commitments with range proofs, and the design needs no trusted setup. Owners can give third parties view keys that show their incoming transactions, or incoming and outgoing ones, for accounting or audits.

Spark is the fourth privacy design on the chain. Zcoin used Zerocoin, which relied on a trusted setup, until Sigma replaced it in July 2019; Lelantus followed in January 2021; and Lelantus coins held before Spark had to be redeemed by block 1,223,500, about 20 December 2025, after which, the project said, they would become inaccessible. On the network, nodes relay new transactions with Dandelion++, which delays and randomises their spread to make the first broadcaster harder to find, and Firo can be run over Tor.

Firo does not hide everything. Transactions to and from transparent addresses are as public as Bitcoin's, including the transparent side of coins moved into Spark and Spark payments to a transparent address such as an exchange deposit. A Spark spend hides its coin among the coins of one set rather than every coin on the chain. In August 2026 a researcher showed that multi-input Spark spends could forge coins; the project limited Spark spends to a single input, warned that single-input spends could reveal amount correlations, and set a hard fork at block 1,371,000, about 4 September 2026, to restore multi-input spends with a new spend format.

Market cap over time

Firo has no TVL: it is a coin with its own blockchain, so the chart shows its market cap. Daily market cap from Coin Metrics Community Data (CC BY-NC 4.0) since 1 Mar 2023, and the current value from DefiLlama. The latest value is from 28 Oct 2026, 00:00 UTC. The series is in protocol-firo.json, listed on the Data page.

What it hides and what it does not

What it hides

  • The sender, the receiver and the amount of Spark transactions, the default way to send and receive FIRO in the official wallets since Spark activated on 18 January 2024.
  • Which earlier coin a Spark spend consumes: a one-out-of-many proof shows only that it is one of a set of Spark coins, which Firo's code caps at 32,000.
  • Spark addresses, which cannot be looked up on a blockchain explorer.

What it does not hide

  • Transactions to and from transparent addresses, which remain available beside Spark and are as public as Bitcoin's, including the transparent side of coins moved into Spark and Spark payments to a transparent address such as an exchange deposit.
  • The real coin against the whole chain: a spend hides it among the coins of one anonymity set, at most 32,000, not among every coin ever created.
  • Amount correlations in single-input Spark spends, which the project warned of while multi-input spends were disabled after the flaw disclosed in August 2026.
  • The IP address of a wallet or node to the peers it connects to and to its internet provider, unless it is run over Tor: Dandelion++ relay only makes the first broadcaster of a transaction harder to find.

Drawn from how it works, above; the sources are listed at the end of the page. Where privacy still leaks explains the patterns, such as timing and amounts, that can give users of any design away.

Audits

Six security reviews, oldest first, with what each covered and found. Dates are when each report was issued, unless the entry says otherwise.

DateFirmScope and findings
Trail of Bits

Lelantus cryptographic library, reviewed by engineers Jim Miller and Will Song; the library largely complied with the specification, with one medium-severity and one informational issue, and a high-severity issue was found in unfinished integration code. Funded mostly by 105 community contributions totalling 5,569.55 XZC, with the rest from the development fund.

Sources: Lelantus Cryptographic Library Audit Results Firo, 13 Aug 2020; Zcoin Lelantus summary report Trail of Bits (GitHub)
Not dated ABDK Consulting (Dmitry Khovratovich)

Cryptography of the Lelantus protocol rather than its implementation, paid for by the development fund; in August 2020 Zcoin expected the results within one to two weeks, and the report on Firo's research page carries no date.

Sources: Lelantus Cryptographic Library Audit Results Firo, 13 Aug 2020; Lelantus cryptography audit (ABDK Consulting) Firo
HashCloak

Cryptography of the Lelantus Spark paper, reviewed by Mikerah Quintyne-Collins and her team; no issues were found in relation to counterfeiting of coins or loss of transaction privacy, and errors found in the paper were fixed. Funded jointly by the community and core team funds.

Sources: Lelantus Spark Audit Complete Firo, 4 Jan 2022; Lelantus Spark Audit Report Firo
Not dated Daniel (Linfeng) Zhao

A second cryptography audit of Lelantus Spark, listed on Firo's research page with its report; the page gives no date or findings summary.

Sources: Lelantus Spark cryptography audit (Linfeng Zhao) Firo; Research Firo, 23 Oct 2026
HashCloak

Firo's Lelantus Spark implementation, audited from 24 October to 28 November 2022, with an initial report on 9 December and the final report, noting the core team's fixes, on 19 December 2022; no critical or high-severity issues were found and all other findings were resolved. Cost USD 80,000, funded by the community.

Sources: Lelantus Spark Code Audit Completed Firo, 20 Dec 2022; Lelantus Spark code audit report Firo
Cypher Stack, with HashCloak

Review, with the Firo core team, of the fix for the multi-input Spark forgery flaw disclosed in August 2026, released as a new versioned Spark spend format in v0.14.18.0; the project said the earlier cryptography and code audits had not caught the flaw. No separate report was published with the release.

Sources: Firo v0.14.18.0 Released: Spark Functionality to be Fully Restored Firo, 27 Aug 2026; Spark Vulnerability Mitigated Firo, 13 Aug 2026

Incidents

Ten incidents, oldest first: flaws, exploits, sanctions, prosecutions and other events that affected the project or its users.

  1. Exploit

    Zcoin announced that one extra character in its Zerocoin code had let an attacker reuse valid proofs to make extra spends; the team estimated that about 370,000 XZC were created and almost all sold, for a profit of about 410 BTC, and said the bug was not a weakness in the cryptography and had not compromised anonymity, according to The Hacker News.

    Source: A Typo in Zerocoin's Source Code helped Hackers Steal ZCoins worth $585,000 The Hacker News, 18 Feb 2017

  2. Exploit

    Zcoin was alerted to irregular Zerocoin mint and spend patterns, traced them by 19 April to a flaw in one of Zerocoin's zero-knowledge proofs that let one mint be spent many times, and released an emergency update on 24 April, disabling Zerocoin instead of fixing it; CryptoSlate reported that about 1% of circulating supply had been forged.

    Source: Zerocoin exploit found, Zcoin attacked, other privacy coins at risk CryptoSlate, 28 Apr 2019

  3. Upbit in South Korea ended trading in Zcoin (XZC/BTC) at 11:00 KST under a notice of 8 May 2020 citing the project's anonymous-transaction aims, having designated it an investment-warning asset and stopped deposits on 29 April.

    Sources: [Market] Termination of trading support (5 projects) - GRS, IOTX, KMD de-flagging from Investment warning (notice 1266) Upbit, 8 May 2020; 디지털 자산 유의 종목 지정 안내 (8종) (Investment warning designation of 8 digital assets, notice 1254) Upbit, 29 Apr 2020

  4. Exploit

    A 51% attack replaced about a day of blocks, rolling back more than 300, mainly to take funds from exchanges: Binance reported losses of 906,771 FIRO and Indodax 82,741 FIRO. The team temporarily disabled Lelantus with its emergency switch, froze the attacker's proceeds, limited reorganisations to five blocks and brought forward ChainLocks.

    Source: Firo 51% attack post mortem and vote on attackers' funds Firo community forum, 22 Jan 2021

  5. Exploit

    After irregular behaviour and suspicious transactions in Lelantus, the team switched it off with the emergency switch and worked with Trail of Bits, cryptographer Sarang Noether and a black hat to find the cause; Lelantus was re-enabled after a hard fork at block 365,544 with Firo v14.6.0, which the project announced on 26 April 2021. No figure for coins created was published in the sources found.

    Sources: Lelantus disabled temporarily Firo community forum, 26 Feb 2021; Lelantus reactivated on Firo Firo, 26 Apr 2021; firo_params.h (ZC_LELANTUS_FIXES_START_BLOCK) Firo (GitHub), 23 Oct 2026

  6. Huobi Global delisted FIRO with DASH, DCR, XMR, XVG, ZEC and ZEN, having ended trading on 6 September and closed deposits on 12 September 2022; HTX's API gives 22 December 2022 as the trade-open time of a new FIRO/USDT market.

    Sources: Huobi Global to Delist DASH, DCR, FIRO, XMR, XVG, ZEC, and ZEN (Internet Archive copy of 2022-09-13) Huobi Global, 12 Sep 2022; HTX spot API: all supported trading symbols (v2) HTX, 13 Oct 2026

  7. Binance users in France, Italy, Poland and Spain could no longer buy or trade FIRO and XMR, with BEAM, MOB and ZEN, The Block reported; Belgian users followed in September 2023.

    Sources: Binance to block privacy coins in four European countries The Block, 31 May 2023; Binance reverses decision on privacy coin trading in EU The Block, 26 Jun 2023; Binance moves to delist privacy coins in Belgium The Block, 6 Sep 2023

  8. Binance ended spot trading in FIRO at 03:00 UTC with 13 other tokens from the first batch of its Vote to Delist, announced on 8 April 2025, after adding FIRO to its Monitoring Tag list on 4 January 2024.

    Sources: Binance Announced the First Batch of Vote to Delist Results and Will Delist FIRO and 13 other tokens on 2025-04-16 (title shortened) Binance, 8 Apr 2025; Binance Will Extend the Monitoring Tag to Include ANT, FIRO, KP3R, MDX, MOB, REEF, VAI, XMR, ZEC & ZEN, and Remove the Seed Tag for GMX & SUSHI on 2024-01-04 Binance, 4 Jan 2024

  9. HTX ended FIRO trading at 07:00 UTC, citing low trading volume, under a notice of 16 September 2025 that kept withdrawals open until 19 September 2027.

    Source: HTX to Delist AZERO, ELIZA, ERG, ERTHA, FIRO, HGG, KMD, LUCE and WLKN HTX, 16 Sep 2025

  10. Carter Annandale reported through responsible disclosure that an attacker could forge Spark coins in multi-input transactions, and Giap Vu reported the same flaw on 6 August. Apart from about 200 FIRO the researcher generated on mainnet to test it, the project said on 13 August that it had found no evidence of inflation; v0.14.17.2 limited Spark spends to one input until the v0.14.18.0 hard fork.

    Sources: Spark Vulnerability Mitigated Firo, 13 Aug 2026; Firo v0.14.18.0 Released: Spark Functionality to be Fully Restored Firo, 27 Aug 2026

Milestones

13 milestones, oldest first.

  1. Zcoin launched, using the Zerocoin protocol for private transactions.

    Source: Happy 6th Birthday Firo Firo, 28 Sep 2022

  2. Sigma replaced Zerocoin at block 184,200, removing Zerocoin's trusted setup and cutting proofs from about 25 kB to 1.5 kB; holders could convert Zerocoin mints to Sigma.

    Sources: What is Sigma and why is it replacing Zerocoin in Zcoin? Firo, 20 Mar 2019; Sigma is released Firo, 10 Jul 2019; Privacy coin Zcoin's new protocol launches on mainnet The Block, 30 Jul 2019

  3. The first halving ended the founders' and seed investors' share of the block reward, and a 15% development fund began.

    Source: Block reward allocation and development fund for the next 4 years Firo, 4 May 2020

  4. Zcoin became Firo, ticker FIRO, on the same blockchain, a change announced on 27 October 2020.

    Sources: Zcoin is becoming Firo Firo, 27 Oct 2020; Rebrand is live Firo, 30 Nov 2020

  5. Lelantus, which hides the origins and amounts of transactions, activated at block 336,888.

    Sources: Lelantus activating on Firo Firo, 6 Jan 2021; firo_params.h (ZC_LELANTUS_STARTING_BLOCK) Firo (GitHub), 23 Oct 2026

  6. ChainLocks, signed by masternode quorums, were scheduled to activate at block 341,100, brought forward after the 51% attack of 18 January.

    Source: Firo 51% attack post mortem and vote on attackers' funds Firo community forum, 22 Jan 2021

  7. FiroPoW, based on ProgPoW 0.9.4, replaced the MTP mining algorithm, and InstantSend was activated, with Firo v0.14.9.0.

    Sources: FiroPoW and InstantSend Release with Firo v0.14.9.0 Firo, 1 Oct 2021; Happy 6th Birthday Firo Firo, 28 Sep 2022

  8. The block time was cut to two and a half minutes.

    Source: Happy 6th Birthday Firo Firo, 28 Sep 2022

  9. Lelantus Spark activated at block 819,300, and Spark addresses became the default way to send and receive FIRO in the official wallets.

    Sources: Lelantus Spark Binary Release Firo, 27 Nov 2023; Spark is live Firo, 18 Jan 2024; firo_params.h (SPARK_START_BLOCK) Firo (GitHub), 23 Oct 2026

  10. A hard fork at block 958,655 set the block reward division at 70% masternodes, 5% miners, 15% development and 10% community, with a fixed emission of 6.25 FIRO per block until the 21.4 million cap.

    Source: Finalized Tokenomics 2024 Firo, 1 Sep 2024

  11. Spark Names, human-readable aliases for Spark addresses, activated on mainnet.

    Source: Spark Names activated Firo, 28 May 2025

  12. The window to redeem Lelantus coins held before Spark was set to close at block 1,223,500, after which unredeemed coins would become inaccessible.

    Sources: Lelantus V1.0 Redemption Period Closing Soon Firo, 28 Nov 2025; firo_params.h (LELANTUS_GRACEFUL_PERIOD) Firo (GitHub), 23 Oct 2026

  13. The v0.14.18.0 hard fork was set to activate at block 1,371,000, restoring multi-input Spark spends with a new versioned spend format that fixes the August 2026 forgery flaw.

    Source: Firo v0.14.18.0 Released: Spark Functionality to be Fully Restored Firo, 27 Aug 2026

Funding

Four sources of funding, oldest first. Amounts are in US dollars; a dash means the sources give no US dollar figure.

DateRoundAmountInvestors

Zcoin Crowdfunding System campaign for the Trail of Bits audit of the Lelantus library: 105 contributions totalling 5,569.55 XZC, with the balance from the development fund

Source: Lelantus Cryptographic Library Audit Results Firo, 13 Aug 2020

 – Community donors (105 contributions)

Development fund: 15% of block rewards from the September 2020 halving, with 35% to masternodes (then Znodes) and 50% to miners, ending the founders' and seed investors' rewards (paid in XZC, so no fixed US dollar amount)

Source: Block reward allocation and development fund for the next 4 years Firo, 4 May 2020

 – –

Community-funded audit: HashCloak's code audit of Lelantus Spark, with MAGIC Grants helping to cover the milestone payments

Source: Lelantus Spark Code Audit Completed Firo, 20 Dec 2022

 $80,000 Firo community donors, MAGIC Grants

Block reward division from block 958,655: 15% to the development fund and 10% to the community fund, with 70% to masternodes and 5% to miners (previously 50% and 25%), at 6.25 FIRO per block until the 21.4 million cap (paid in FIRO, so no fixed US dollar amount)

Source: Finalized Tokenomics 2024 Firo, 1 Sep 2024

 – –

Risks

Firo's privacy code has failed several times: a one-character bug in 2017 let an attacker create about 370,000 XZC, a flaw in Zerocoin's cryptography in 2019 was used to forge about 1% of supply, Lelantus was switched off from February to April 2021 after suspicious transactions, and in August 2026 a researcher showed that multi-input Spark spends could forge coins, a flaw that the earlier cryptography and code audits had not caught; the project said it had found no evidence of inflation beyond the researcher's test of about 200 FIRO and was monitoring supply. Privacy is optional, so funds that pass through transparent addresses, including deposits to exchanges, can be traced, and a Spark spend hides its coin among at most 32,000 others rather than the whole chain. The proof-of-work chain was rolled back by more than 300 blocks in January 2021; ChainLocks, signed by masternode quorums, now guard against such rollbacks, which makes masternodes, paid 70% of block rewards since September 2024, part of the chain's security. Access through large exchanges has narrowed: Upbit, Huobi, Binance and HTX have delisted FIRO, Binance restricted it in four EU countries in 2023, and from 10 July 2027 the EU's Anti-Money Laundering Regulation will bar crypto-asset service providers from keeping accounts that allow transactions to be anonymised or obscured, including through anonymity-enhancing coins.

Sources

The documents this profile rests on. Each audit, incident, milestone and funding round above also links its own sources.

Checked on 23 Oct 2026. Confidence: confirmed. Information only, not investment, legal or tax advice.

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