It's possible using Electrum's console.
But it's not necessary to use your private key for decryption.
If you want to try, let's just use this address' public key: 1HZwkjkeaoZfTSaJxDw6aKkxp45agDiEzN (
leaked brainwallet address)
04a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd5b8dec5235a0f a8722476c7709c02559e3aa73aa03918ba2d492eea75abea235Follow this syntax
encrypt('public key', 'message to encrypt'),
example:
encrypt('04a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd5b8dec5235a0fa8722476c7709c02559e3aa73aa03918ba2d492eea75abea235', 'Test message to a leaked brainwallet')
The result is this encrypted message:
"QklFMQNS2Vu/26J7IFisRNH1tfkeUN4lUpOTp+vxuYrmA8cSFWlsqVCnAgjFgsXPXJDC5ihC2KmJs+fm5zgPF/2/DUmnU/t50Tz6tse57diRZ6Byt4K49ZLSKtV53MHommmjDgPA4oabgIx7xLkFmZDH6bAr"
This should be given to the other party who already knew your public key.
Then he should use this syntax to decrypt the message
decrypt('public key', 'encrypted message');
for the example above:
decrypt('04a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd5b8dec5235a0fa8722476c7709c02559e3aa73aa03918ba2d492eea75abea235', "QklFMQNS2Vu/26J7IFisRNH1tfkeUN4lUpOTp+vxuYrmA8cSFWlsqVCnAgjFgsXPXJDC5ihC2KmJs+fm5zgPF/2/DUmnU/t50Tz6tse57diRZ6Byt4K49ZLSKtV53MHommmjDgPA4oabgIx7xLkFmZDH6bAr")
Will result into: "Test message to a leaked brainwallet".
Manually highlight & copy the codes 'cause sometimes, a space will appear at the end if you double clicked it.