Private keys are long strings of letters and numbers that are literally the key to spending your bitcoin. Each wallet has a number of private keys (one for each address). You can back up your private keys for a MultiBit Classic wallet into a text file called a 'private key export file'. You can password protect this text file to prevent other people reading this data.
Below is an example of a private key export file containing demonstration private keys. You typically use Notepad or similar when working with this file.
# KEEP YOUR PRIVATE KEYS SAFE ! # Anyone who can read this file can spend your bitcoin. # # Format: # <Base58 encoded private key>[<whitespace>[<key createdAt>]] # # The Base58 encoded private keys are the same format as # produced by the Satoshi client/ sipa dumpprivkey utility. # # Key createdAt is in UTC format as specified by ISO 8601 # e.g: 2011-12-31T16:42:00Z . The century, 'T' and 'Z' are mandatory # Labc123abc123abc123abc123abc123abc123abc123abc123abc 2013-01-01T12:00:00Z Kdef456def456def456def456def456def456def456def456def 2013-01-01T12:00:00Z # End of private keys
The key (shown in bold) begins with either "L" or "K". The date is there to allow import software to know when the key was created to avoid looking further back in history than is necessary. Don't change the date to be more recent as doing so will very likely cause a failed import and an incorrect balance.
Below is an example of a password protected private key export file containing demonstration private keys. You typically use MultiBit Classic or OpenSSL when working with this file.
U2FsdGVkX1+YqTr9vabcfVlfKlCVTjR7kEg/xD4rEUB1tBBQm6chWSOSIUyJKK/9yjxFSHkge/xI UCFq3MfFKqUbRnYcmOhNLBabcGRrbvsx3AawNvzp1sdHFXNvH3I+INMtYaoTjMEJVkQM8KnaUwZI GE5PYKtMHncv+2pYA1/3Lg09hPA++jbvwL7L+NH6ZcljvYZxseu+3M45YNK1CJ/4xQJ+Yvo6OVqJ nL7xIR0=
The content is encrypted (AES256, password-based key derivation) so can only be decrypted by special software and the provision of a password.
The MultiBit Classic wiki provides detailed technical information about the file format.
If you are intending to store exported keys for a very long time and are concerned about code existing to open them far in the future then we recommend the following: