When generating a seed in 2.7.x there is now an option to "extend this seed with custom words".
Is there a maximum allowable length of characters for the entire string of "custom words"?
Can I use special characters in the "custom words"?
Does it matter if I input special characters in other encodings besides UTF-8?
I believe electrum uses BIP39 for the seed generation and found this about its spec.
Is there a maximum allowable length of characters for the entire string of "custom words"?
Can I use special characters in the "custom words"?
Does it matter if I input special characters in other encodings besides UTF-8?
I believe electrum uses BIP39 for the seed generation and found this about its spec.
Quote
From mnemonic to seed
A user may decide to protect their mnemonic with a passphrase. If a passphrase is not present, an empty string "" is used instead.
To create a binary seed from the mnemonic, we use the PBKDF2 function with a mnemonic sentence (in UTF-8 NFKD) used as the password and the string "mnemonic" + passphrase (again in UTF-8 NFKD) used as the salt. The iteration count is set to 2048 and HMAC-SHA512 is used as the pseudo-random function. The length of the derived key is 512 bits (= 64 bytes).
A user may decide to protect their mnemonic with a passphrase. If a passphrase is not present, an empty string "" is used instead.
To create a binary seed from the mnemonic, we use the PBKDF2 function with a mnemonic sentence (in UTF-8 NFKD) used as the password and the string "mnemonic" + passphrase (again in UTF-8 NFKD) used as the salt. The iteration count is set to 2048 and HMAC-SHA512 is used as the pseudo-random function. The length of the derived key is 512 bits (= 64 bytes).
If you are generating the new wallet in a safe OS, keep your seeds safe in different places there's no need to experiment with adding custom words. Electrum is very strong as it is now and probably I never heard a hack story about it, only user forgetting their seeds. So I would say Electrum is at the top of the security in the desktop wallets area.
