Introduction

Ledger signers isolate cryptographic secrets, such as PGP or Bitcoin private keys, from a potentially insecure computer. Storing these secrets on a physical medium that a virus cannot infect, such as paper or an encrypted drive, is secure until you need to use your funds.

To transfer funds, you need to sign the transaction. Loading your private keys onto your computer for this purpose exposes them to potential malware. The alternative is to perform the required cryptographic operations by hand, which is impractical.

Signers address this problem. They store your cryptographic secrets and let you use them securely for operations such as signing transactions. Ledger signers also use an AIS-31-compliant true random number generator (TRNG) to generate secrets with a large amount of entropy. Using these internally generated secrets is more secure than importing a secret that may have been compromised before it reached the signer.

Ledger uses Secure Element technology to build signers that connect people with cryptocurrencies and blockchains. The Secure Element protects your private keys from tampering and eavesdropping. The screens on the Ledger Nano X and Nano S Plus also provide a trusted source of information about your assets. The signer controls the screen, rather than potentially vulnerable computer software.

Signers are not intended to store data. Instead, they provide a root of trust. Signer apps tend to be lightweight and work with a host computer. Because the Secure Element limits storage capacity, it is preferable to store encrypted data on the host computer rather than directly on the signer. The signer holds private keys that you can use to unlock your data and assets. If your computer becomes infected with a virus, those keys remain protected.

Applications that process large amounts of data may not be able to store all the data on the signer at once. One approach is to stream data through the signer while the application processes it, for example, by encrypting or decrypting the data. Alternatively, an application can derive a secret on the signer, preferably from the master seed, and use it on the computer to process the data. This is how the PGP app  works.

The key concept is that a signer provides a secure portal to your assets; it is not a bank. If you lose or destroy your signer, your assets remain safe. Your master seed is the key to this portal. The next section explains The Master Seed.