npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! [email protected] postinstall: `node install.js`
npm ERR! Exit status 1
The official blockchain.info decryption tool is written in Node so it's possible that you're actually having errors getting the Node app to start (maybe you're running it wrong? )
Or you didn't use correct Node and npm version mentioned on the GitHub repository. But they also prepare compiled version on release page (https://github.com/blockchain/my-wallet-backup-decryption-tool/releases). I checked Windows version and there's .exe file, so it should be easier for you to try (i didn't run it because i currently use different OS).