What is a Seed Phrase? Complete Guide to Cryptocurrency Recovery Phrases
📋 En bref (TL;DR)
- Definition: a seed phrase is a sequence of 12 or 24 words that allows you to recover all your cryptocurrencies
- How it works: it mathematically encodes all your private keys according to the BIP39 standard
- Critical importance: if you lose it, your funds are lost forever; if someone obtains it, they can steal everything
- Storage: always on physical media (paper, metal), never digital (photo, cloud, email)
- Key takeaway: it’s your only recovery point, protect it like you would protect a vault
In the cryptocurrency universe, the seed phrase represents the master key to your digital wealth. This seemingly innocuous sequence of words holds absolute power: it can regenerate all your private keys and thus recover access to all your cryptocurrencies.
Unlike traditional banking systems where you can reset a forgotten password, there is no customer service, no recourse if you lose your seed phrase. It is your only recovery point, your ultimate safety net.
What is a seed phrase?
A seed phrase (also called recovery phrase or mnemonic phrase) is a sequence of 12 or 24 words that mathematically encodes all the private keys of your crypto wallet. These words are drawn from a standardized dictionary of 2048 words defined by the BIP39 standard, and allow you to restore access to all your funds on any compatible wallet.
Essential characteristics:
- Standardized length: 12, 15, 18, 21, or 24 words (12 and 24 being the most common)
- BIP39 dictionary: words drawn from a list of 2048 words available in multiple languages
- Human-readable format: designed to be easily transcribed and memorized, unlike hexadecimal private keys
- Multiple generation: a single seed phrase can create billions of different crypto addresses
Example seed phrase (never use this example):
abandon ability able about above absent absorb abstract absurd abuse access accident
How does a seed phrase work?
The seed phrase works as a cryptographic seed: from these words, a deterministic mathematical algorithm generates all your private and public keys. The same set of words will always produce the same keys, on any device and any BIP39-compatible wallet.
The BIP39 standard
BIP39 (Bitcoin Improvement Proposal 39) is the standard that defines how seed phrases are created and used:
- Entropy generation: the wallet generates a random sequence of 128 to 256 bits
- Checksum calculation: a SHA-256 hash is calculated to verify integrity
- Word conversion: the binary sequence is divided into 11-bit segments, each corresponding to a word from the dictionary (2^11 = 2048 possible words)
- Key derivation: the seed phrase is converted to a binary seed via PBKDF2, then keys are derived according to BIP32/BIP44
From seed phrase to addresses
The derivation process is hierarchical and deterministic (HD – Hierarchical Deterministic):
Seed phrase → Binary seed (512 bits) → Master key → Child keys → Public addresses
This architecture allows managing thousands of different addresses (Bitcoin, Ethereum, and others) from a single seed phrase, while maintaining the ability to restore everything with these 12 or 24 words.
Seed phrase, private key, and wallet: what are the differences?
The seed phrase is the root of everything: it generates your private keys, which in turn control your public addresses. These three elements form a security hierarchy that is essential to understand.
| Element | Description | Role |
|---|---|---|
| Seed phrase | 12-24 readable words | Master backup, complete restoration |
| Private key | 256-bit hexadecimal number | Signs transactions, proves ownership |
| Public key | Derived from the private key | Generates receiving addresses |
| Wallet | Software or device | Interface to manage your keys and transactions |
Crucial point: your cryptocurrencies are not “in” your wallet. They are on the blockchain. The wallet only stores the keys that prove you own them. The seed phrase allows regenerating these keys on any compatible wallet.
Why is the seed phrase so important?
The seed phrase is the only way to recover your funds if your wallet is lost, stolen, or destroyed. Without it, your cryptocurrencies become permanently inaccessible — there is no recovery procedure.
Permanent loss scenarios
- Lost or stolen phone without seed phrase backup → funds lost
- Hardware wallet failure without seed phrase → funds lost
- Computer crash with desktop wallet → funds lost without seed phrase
- Forgotten wallet password → recoverable only with the seed phrase
Personal responsibility
In traditional finance, your bank can reset your access. In crypto, you are your own bank. This freedom comes with total responsibility: no one can help you if you lose your seed phrase.
It is estimated that 20% of bitcoins in circulation (approximately 3.7 million BTC) are permanently lost, mainly due to misplaced seed phrases or seed phrases that were never backed up.
How to properly back up your seed phrase?
The golden rule: your seed phrase should NEVER exist in digital form. No photo, no text file, no cloud, no email. Only physical media.
Recommended methods
1. Paper (basic method)
- Write legibly on quality paper
- Use permanent ink (not pencil)
- Store in a dry place, away from light
- Make multiple copies stored in different locations
2. Metal (recommended method for long-term)
- Stainless steel or titanium plates (Cryptosteel, Billfodl, etc.)
- Fire-resistant up to 1500°C, waterproof, corrosion-resistant
- Investment of $50-150 for maximum protection
3. Safe or bank vault
- For significant amounts
- Protects against theft and household disasters
- Consider a bank safe deposit box for a backup copy
What you should never do
- Take a photo of the seed phrase
- Save it in a file (even encrypted)
- Send it by email, SMS, or messaging
- Store it in an online password manager
- Back it up on cloud storage (Google Drive, iCloud, Dropbox)
- Share it with anyone
Threats and scams to know about
The seed phrase is the primary target of hackers and scammers. Anyone who obtains it can instantly drain all your wallets. Here are the most common threats.
Phishing
Fraudulent websites imitate popular wallet interfaces and ask for your seed phrase for “verification” or an “update.” Absolute rule: no legitimate service will ever ask you for your seed phrase.
Fake technical support
Scammers impersonate MetaMask, Ledger, or other wallet support on social media. They contact users having problems and ask for the seed phrase to “resolve” the issue.
Malware and keyloggers
Malicious software can record what you type or scan your files looking for seed phrases. This is why you should never enter it on a potentially compromised computer.
Pre-generated seed phrases
Some scammers sell wallets with a seed phrase already set up, which they secretly retain. Once the victim deposits funds, they steal them. Always generate your seed phrase yourself on a new device.
12 words or 24 words: which to choose?
Both offer a more than sufficient security level, but 24 words provide an additional margin for very large amounts.
| Criterion | 12 words | 24 words |
|---|---|---|
| Entropy | 128 bits | 256 bits |
| Possible combinations | 2^128 ≈ 3.4 × 10^38 | 2^256 ≈ 1.2 × 10^77 |
| Security | Unbreakable in practice | Resistant even to future quantum computers |
| Practicality | Easier to back up | Longer to transcribe |
| Recommended use | Moderate amounts | Large portfolios, long-term storage |
In practice, 12 words already offer an astronomical level of security. Brute-forcing 128 bits would take billions of years even with all the computers on the planet. The 24 words are an additional precaution for those who want a margin against future technological advances.
The passphrase: an additional layer of security
The passphrase (or 25th word) is an optional password that is added to the seed phrase to create an entirely different wallet. It’s an advanced protection against physical theft of your seed phrase.
How it works
With the same seed phrase, each different passphrase generates a completely different set of keys:
- Seed phrase alone → Wallet A
- Seed phrase + passphrase “secure123” → Wallet B (completely different)
- Seed phrase + passphrase “mypassword” → Wallet C (completely different)
Advantages and risks
Advantages:
- If someone finds your seed phrase, they only access the “decoy” wallet (without passphrase)
- You can have a small visible amount and the bulk of your funds protected by passphrase
Risks:
- If you forget the passphrase, the funds are lost (no recovery possible)
- Adds complexity to your backup system
Glossary
- BIP39: standard defining the generation and use of mnemonic seed phrases for crypto wallets.
- Private key: a secret 256-bit number that allows signing transactions and proving ownership of funds.
- Hierarchical derivation (HD): method allowing the generation of multiple keys from a single seed, according to BIP32/BIP44 standards.
- Entropy: measure of the randomness of data. The higher the entropy, the more secure the seed phrase.
- Passphrase: optional password added to the seed phrase to create a different wallet (25th word).
- HD Wallet: hierarchical deterministic wallet capable of generating an infinite number of addresses from a single seed.
Frequently Asked Questions
Can I change my seed phrase?
No, a seed phrase cannot be modified. If you want a new seed phrase, you must create a new wallet and transfer your funds to it. The old wallet will remain accessible with the old seed phrase.
What should I do if someone has seen my seed phrase?
Immediately transfer all your funds to a new wallet with a new seed phrase. Consider the old wallet compromised, even if no theft has occurred yet.
Does my seed phrase work on all wallets?
If your wallet uses the BIP39 standard (the vast majority), your seed phrase will work on any other BIP39-compatible wallet. Some older wallets use proprietary non-compatible formats.
Can I memorize my seed phrase instead of writing it down?
It’s risky. Human memory is fallible, especially over several years. Even if you memorize it, always keep a secure physical backup.
How many copies of my seed phrase should I make?
At minimum 2 copies, stored in geographically distinct locations (e.g., home + bank vault, or with two trusted family members). The more significant your funds, the more redundancy is justified.
Do hardware wallets have a seed phrase?
Yes, all hardware wallets (Ledger, Trezor, etc.) generate a seed phrase during initialization. It is this seed phrase that allows you to restore your funds if the device is lost or damaged.
Sources
- BIP39 – Mnemonic code for generating deterministic keys – Official technical specification
- Bitcoin Wiki – Seed phrase – Bitcoin community documentation
- Ledger Academy – What is a recovery phrase – Hardware wallet manufacturer guide
How to cite:
Fibo Crypto. (2026). What is a Seed Phrase? Complete Guide to Cryptocurrency Recovery Phrases. Retrieved from https://fibo-crypto.fr/en/blog/what-is-seed-phrase-complete-guide
