Two New Heavyweight Features

CCC: COLDCARD can now Co-sign like collaborative multisig HSMs, no centralized servers needed.

KeyTeleport: Send secrets on a video call to other COLDCARD! Securely move seeds, secure notes/passwords, multisig PSBTs, even full backups (full clone), between two Q using QR or NFC

CCC - ColdCard Cosign

COLDCARD holds a key in a 2-of-3 multisig, in addition to the normal signing key it has.

• It applies a spending policy like an HSM:

  • velocity and magnitude limits

  • whitelisted destination addresses

  • 2FA authentication using phone app (RFC 6238)

• But will sign its part of a transaction automatically if those condition are met, giving you 2 keys of the multisig and control over the funds

• Spending policy can be exceeded with help of the other co-signer (3rd key), when needed

• Cannot view or change the CCC spending policy once set, policy violations are not explained

• Existing multisig wallets can be used by importing the spending-policy-controlled key

• CCC Demo Video (youtube) and Online docs (coldcard.com)

Key Teleport (Q)

Easily and securely move seed phrases, secure notes/passwords, multisig PSBT files, and even full Coldcard backups, between two COLDCARD Q using QR codes and/or NFC with helper website.

• Can send master seed (words, xprv), anything held in seed vault, secure notes/passwords (singular, or all) and PSBT involved in a multisig to the other co-signers

• Full COLDCARD backup is possible as well, but receiver must be “unseeded” Q for best result.

• In other words, you can clone your Q over a zoom call to another person.

• ECDH to create session key for AES-256-CTR, with another layer of AES-256-CTR using a short password (stretched by PBKDF2-SHA512) inside

• Receiver shows sender a (simple) QR and a numeric code; sender replies with larger BBQr and 8-char password

• See protocol spec in docs/key-teleport.md

• Online docs are coming soon.

• Related website is: keyteleport.com

Teleport of Multisig PSBT

After you sign a multisig PSBT, you have option to “Key Teleport” the PSBT file to any one of the other signers in the wallet. We already have a shared pubkey with them, so the process is simple and does not require any action on their part in advance. Plus, starting in this firmware release, COLDCARD can finalize multisig transactions, so the last signer can publish the signed transaction via PushTX (NFC tap) to get it on the blockchain directly.

Above is an example of the menu shown where you select who should get the PSBT file next. As you can see two have already signed the file (checkmarks).

Shared Improvements - Both Mk4 and Q

• New Feature: Multisig transactions are finalized when sufficiently signed. Allows use of PushTX with multisig wallets.

• New Feature: Signing artifacts re-export to various media. Now you have the option of exporting the signing products (transaction/PSBT) to different media than the original source. Incoming PSBT over QR can be signed and saved to SD card if desired.

• New Feature: Multisig export files are signed now. Read more here

• Enhancement: NFC export usability upgrade: NFC keeps exporting until CANCEL/X is pressed

• Enhancement: Add Bitcoin Safe option to Export Wallet

• Enhancement: 10% performance improvement in USB upload speed for large files

• (Q only) Enhancement: Always choose the biggest possible display size for QR

Bugfixes

• Do not allow change Main PIN to same value already used as Trick PIN, even if Trick PIN is hidden.

• Fix stuck progress bar under Receiving... after a USB communications failure

• Showing derivation path in Address Explorer for root key (m) showed double slash (//)

• Can restore developer backup with custom password other than 12 words format

• Virtual Disk auto mode ignores already signed PSBTs (with “-signed” in file name)

• Virtual Disk auto mode stuck on “Reading…” screen sometimes

• Finalization of foreign inputs from partial signatures. Thanks Christian Uebber!

• Temporary seed from COLDCARD backup failed to load stored multisig wallets

• Destroy Seed also removes all Trick PINs from SE2.

• Lock Down Seed requires pressing confirm key (4) to execute

• (Q only) Only BBQr is allowed to export Coldcard, Core, and pretty descriptor

Download the latest firmware

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Bitcoin is always evolving and there are many powerful new features that are “just around the corner”. We want to get closer to that corner, and make that new tech safe to use! But at the same time, we’re not sure if it is safe yet. It’s got bugs for sure, and some of those bugs might be very expensive.

Our answer is what we’re calling “Edge Firmware for Mk4”. It will be updated more frequently and contain the very latest in BIP’s and other upcoming tech for Bitcoin. It’s not for everyday hodlers: it’s for the wallet developers and power users who are itching to experiment with new types of signatures, and complex new on-chain wallet types.

Let’s not be #reckless — Do not use this firmware on your main stash. Do not run it to impress potential sexual partners.

Winning features from “edge” will be moved to the normal firmware only when they are ready, and we are still developing new and practical features on both branches. Isolating the riskier stuff allows us to concentrate on everyday features, that everyone can use right away, while the Bitcoin community develops supporting code for new types of signatures and consensus related changes.

If you are not a developer, you can ignore Edge version completely.

Where to Find It

The source code lives on branch edge on the same Coldcard github repo: Edge branch on Github

Binaries can be reproduced from the code in that branch and signed binaries will carry an X in their version number. The code will alert the user on each power up, and the scroll bar is marked with “EDGE”, on screen.

Get the signed binary here

6.0.0X - First Edge release.

TAPROOT

• Taproot keyspend & Tapscript multisig sortedmulti_a (tree depth = 0)

• Paper wallets can be P2TR address format.

• Limitations:

  • only TREE of depth 0 is allowed

  • max 32 signers in TR multisig, only allowed script is: sortedmulti_a

  • if we can sign by both key path and script path: key path has precedence.

• Full technical details available here.

BIP-0129 Bitcoin Secure Multisig Setup (BSMS)

• Both Coordinator and Signer roles are supported.

• Encryption and decimal and hex tokens are supported.

• More screenshots and user documentation.

Fixes & Common Enhancements

• Enhancement: change Key Origin Information export format in multisig addresses.csv according to BIP-0380 (m=0F056943)/m/48'/1'/0'/2'/0/0 –> [0F056943/48'/1'/0'/2'/0/0]

• Bugfix: correct scriptPubkey parsing for segwit v1-v16

• Bugfix: do not infer segwit just by availability of PSBT_IN_WITNESS_UTXO in PSBT

These have been fixed on master as well, but are not yet part of a release.

What’s Next

Obviously… Miniscript!

Download the latest firmware

Get COLDCARD Mk4

We are thrilled to introduce a new member of the Coinkite family! Please join us in extending a warm welcome to Vivek, our newly appointed Vice President of Business Development.

With extensive industry knowledge and experience under his belt, Vivek is eager to share his expertise with you. He will be embarking on a nationwide tour, conducting workshops to help you fully harness the power of Coinkite's comprehensive product suite, including the indispensable COLDCARD. Recognizing the importance of the COLDCARD to the Bitcoin community, we are committed to equipping our users with all the necessary resources for maximizing its potential.

We'd love to hear from you! Share your suggestions for COLDCARD tutorials you'd like Vivek to create by participating in this Twitter thread:

V@Seardsalmon

I heard y’all wanted some @COLDCARDwallet @TAPSIGNER tutorials 😎

5:17 PM · Mar 23, 2023

---

4 Reposts · 54 Likes

—The Coinkite Team

Download the latest firmware

New Features

• “MicroSD card as Second Factor”. Specially marked MicroSD card must be already inserted when (true) PIN is entered, or else seed is wiped. Add, remove and check cards in menu: Settings -> Login Settings -> MicroSD 2FA

• Import TAPSIGNER encrypted backup as main or ephemeral seed, for PSBT signing. This is a great way to safely use the key previously held inside a TAPSIGNER, because the COLDCARD can take over the signing that used to be done by the card.

• Detached Bitcoin signature files for most exports.

  • Files exported are now signed with a detached signature. Look for a .sig file with the same name, and verify signature with your favourite Bitcoin tools. See “Signed Exports” in docs/msg-signing.mdfor more information.

  • Coldcard can now verify signed files:

    • SD card and Virtual disk Advanced/Tools -> File Management -> Verify Sig File

    • NFC Advanced/Tools -> NFC Tools -> Verify Sig File

  • Learn more here

  • Related new website: Check your Bitcoin signatures here

Enhancements

• Address Explorer:

  • Application-specific derivation paths in Address Explorer -> Applications

  • Bugfix: Change value was ignored when generating addresses file

• Imports:

  • Add import multisig wallet via Virtual Disk

  • Add import extended private key via Virtual Disk and via NFC

  • Import seed in compact/truncated form (just 3-4 letters of each seed word)

  • Import extended private key as ephemeral seed

• Export:

  • Samourai POST-MIX and PRE-MIX descriptor export options added

  • Lily Wallet added

  • Ability to export all supported wallets via NFC (instead of SD card only)

  • Change electrum export file name from ‘new-wallet.json’ to ‘new-electrum.json’

  • Allow export of Wasabi skeleton for Bitcoin Regtest.

• Backup Enhancement:

  • Option to save the backup file’s encryption password for next backup. Then next backup is quick and simple: no need to record yet another 12 words.

• During seed generation from dice rolls, enforce at least 50 rolls for 12 word seeds, and 99 rolls for 24 word seeds. Statistical distribution check

• Single signature wallet generic descriptor export Advanced -> Export Wallet -> Descriptor. Both new format with internal/external in one descriptor <0;1> and standard with two descriptors are supported. added to prevent users from generating low-entropy seeds by rolling same value repeatedly.

• Docs: Add docs/rolls12.py script for verifying dice rolls math for 12 word seeds.

Bug Fixes

• Offer import/export from/to Virtual Disk in UI even if SD Card is inserted.

• Recalculate extended key saved in settings upon chain change (BTC, XTN, XRT).

• Provide correct derivation path (m/84’/1’/0’) for testnet Wasabi export.

• Properly display UX checkmark only if testnet (XTN, XRT) is enabled in Settings- > Danger Zone -> Testnet Mode.

  Get the Mk4