Private Key Formats

A private key can be represented in different formats, all corresponding to the same 256-bit number.

Common Private Key Formats

TypePrefixDescription
HexNone64 hexadecimal digits
WIF5Base58check encoding (base58 with version prefix of 128 and 32-bit checksum)
WIF-compressedK or LSame as WIF but with added suffix 0x01 before encoding

Modern Relevancy of Private Key Formats

  • Early Bitcoin wallets generated independent private keys and required frequent backups.
  • Modern wallets use deterministic wallets, generating all private keys from a single seed value.
  • Deterministic wallets only need a single backup.
  • Security concern: If an attacker acquires a single exported key plus some wallet metadata, they may derive all keys in the wallet.
  • No modern wallets support individual key import/export due to security risks.

Example: Same Key in Different Formats

FormatPrivate Key
Hex1e99423a4ed27608a15a2616a2b0e9e52ced330ac530edcc32c8ffc6a526aedd
WIF5J3mBbAH58CpQ3Y5RNJpUKPE62SQ5tfcvU2JpbnkeyhfsYB1Jcn
WIF-compressedKxFC1jmwwCoACiCAWZ3eXa96mBM6tb3TYzGmf6YwgdGWZgawvrtJ

Each format represents the same key in different ways and can be converted into another format easily.

Compressed Private Keys

  • Misnomer: A "compressed private key" is actually longer than an uncompressed private key.
  • The extra byte (0x01) signals that only compressed public keys should be derived from it.
  • Modern wallets only export WIF-compressed private keys (K or L prefix).
  • Old wallets export WIF (uncompressed) keys (5 prefix).

Example: WIF vs WIF-Compressed

FormatPrivate Key
Hex1E99423A4ED27608A15A2616A2B0E9E52CED330AC530EDCC32C8FFC6A526AEDD
WIF5J3mBbAH58CpQ3Y5RNJpUKPE62SQ5tfcvU2JpbnkeyhfsYB1Jcn
Hex-compressed1E99423A4ED27608A15A2616A2B0E9E52CED330AC530EDCC32C8FFC6A526AEDD01
WIF-compressedKxFC1jmwwCoACiCAWZ3eXa96mBM6tb3TYzGmf6YwgdGWZgawvrtJ

Vanity Addresses

  • Vanity addresses are Bitcoin addresses with custom patterns (e.g., 1LoveBPzzD...).
  • They require generating and testing billions of private keys until a match is found.
  • Security: They are as secure as regular addresses but require brute-force computation.
  • Privacy Risk: They encourage address reuse, which can reduce financial privacy.

Example: Vanity Address Search Times

LengthPatternProbabilityAvg. Search Time (Desktop)
11K1 in 58<1 ms
41Kids1 in 11M1 min
71KidsCha1 in 2.2T3-4 months
101KidsCharit1 in 400Q46,000 years
  • Specialized GPUs are required for patterns longer than 7 characters.
  • Vanity pools exist, where miners generate vanity addresses for a fee.

Paper Wallets (OBSOLETE!)

Warning: Paper wallets are obsolete and dangerous due to security risks.

  • Private keys printed on paper for offline storage.
  • Often include the corresponding Bitcoin address.
  • Risks:
    • Many were compromised by malicious generators.
    • Easily lost, stolen, or destroyed.
    • Should not be used for storing Bitcoin.
    • Better alternative: Hardware wallets & seed phrase backups.

Summary

  • Private keys can be stored in different formats, with WIF and WIF-compressed being common.
  • Modern wallets use deterministic seeds and do not allow individual key import/export.
  • Compressed keys refer to public keys, not private keys.
  • Vanity addresses are impractical for long patterns but were popular in Bitcoin’s early days.
  • Paper wallets are insecure and should be avoided.

For safe Bitcoin storage, use deterministic wallets and hardware devices instead of exporting/importing private keys.