Private key
Private key is random string generated by encryption algorithm to encrypt or decrypt public key. Below is an example: 5KYZdUEo39z3FPrtuX2QbbwGnNP5zTd7yyr2SC1j299sBCnWjss.
Private key is generated completely random with different combination in the 64th power of 16(the 256th power of 2), in which case it is basically impossible to generate two sets of identical private key.
The thing is private is too complicate to restore, thus it comes mnemonic words.
Mnemonic words
Mnemonic words are combined with 12-24 words. Mnemonic words can be used to generate mnemonic words, meanwhile private key can be transferred into mnemonic words according to certain algorithm.
A set of mnemonic words is able to generate numerous private key and this is why with a set of mnemonic words, a user can make full management of all addresses.
Mnemonic words are private key in other form. One wallet can only generate one set of mnemonic words and can’t be modified.
Please do remember to backup your mnemonic words and keep it safe!

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