monero-docs/docs/en/mnemonics/legacy.md

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Legacy Mnemonic Scheme

The legacy mnemonic scheme is the oldest and most widely-used mnemonic scheme in the Monero ecosystem. It comprises a total of 25 words, where the first 24 words are for the seed and the last word is for the checksum. The checksum word is used to verify the correctness of the seed.

The first 24 words are randomly selected from a list of 1626 words described in src/mnemonics/english.h (Wordlists available for other languages can be found in src/mnemonics). The checksum word is selected by calculating the CRC32 checksum index of a string that is made by concatenating the first prefix_lengthed characters of each selected word. The prefix_length is the number of characters to be used from each word to calculate the checksum. In the case of English wordlist, the prefix_length is 3.

Example of calculating the checksum word:

1. Randomly select (don't forget that randomness should be cryptographically secure) 24 words from the wordlist. For example, let's say the chosen words are lush bagpipe stacking mice imitate village gang efficient strained different together vain puck roped pancakes shocking liar moisture memoir sorry syndrome kettle swept dehydrate.
2. Take the first 3 characters of each word and concatenate them. In this case, it will be lusbagstamicimivilganeffstrdiftogvaipucroppansholiamoimemsorsynketswedeh.
3. Calculate the CRC32 checksum of the concatenated string. In this case, the checksum gives us the decimal number 2248614488.
4. Take the checksum index modulo 24. In this case, the modulo gives us 8.
5. The 8th index of the wordlist is strained (don't forget that the wordlist is 0-indexed). So, the checksum word is strained.