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Does BIP39 mnemonic construction avoid repeating words?

up vote 14 down vote favorite

Will all 24 words of a seed-phrase be unique by specification? Or is it possible for a word to occupy two positions (ie the word "tool" is #8 AND #20 in a valid, securely generated seed)

2 Answers

up vote 4 down vote accept

There is nothing stopping a word to be repeated more than once. In a 24 word mnemonic, with 2048 possible words in the dictionary (BIP 39), there is a probability of at least one duplicate around 12.7% of the time (variation of the birthday paradox).

up vote 3 down vote

No, the BIP39 construction does not avoid repeating words.

It is possible for a word to show up multiple times, but since there are 2048 words it is fairly unlikely for repeats to show up in randomly generated keys.


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Does BIP39 mnemonic construction avoid repeating words?

up vote 14 down vote

Will all 24 words of a seed-phrase be unique by specification? Or is it possible for a word to occupy two positions (ie the word "tool" is #8 AND #20 in a valid, securely generated seed)


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up vote 9 down vote

There is nothing stopping a word to be repeated more than once. In a 24 word mnemonic, with 2048 possible words in the dictionary (BIP 39), there is a probability of at least one duplicate around 12.7% of the time (variation of the birthday paradox).

edit

Preventing duplicate words will in fact restrict the entropy of the seed phrase. - pim Oct 23 '17 at 14:34

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