Wallet software usually stores information it needs to operate on the disk of the computer it runs on. If an adversary has access to that disk it can extract bitcoin addresses and transactions which are known to be linked with the owner of that disk. The same disk might contain other personal information (such as a scan of an ID card). Digital forensics is one reason why all good wallet software encrypts wallet files, although that can be beaten if a weak encryption password is used.
For example if you have a bitcoin wallet installed on your PC and give the computer to a repair shop to fix, then the repair shop operator could find the wallet file and records of all your transactions. Other examples might be if an old hard disk is thrown away. Other software installed on the same computer (such as malware) can also read from disk or RAM to spy on the bitcoin transactions made by the user.
For privacy don't leave data on your computer available to others. Exactly how depends on your threat model. Encryption and physical protection are options, as is using special operating systems like Tails OS which does not read or write from the hard drive but only uses RAM, and then deletes all data on shutdown.
A bitcoin wallet contains a collection of key pairs, each consisting of a private key and a public key. The private key (k) is a number, usually picked at random. From the private key, we use elliptic curve multiplication, a one-way cryptographic function, to generate a public key (K). From the public key (K), we use a one-way cryptographic hash function to generate a bitcoin address (A). In this section we will start with generating the private key, look at the elliptic curve math that is used to turn that into a public key, and finally, generate a bitcoin address from the public key.
A private key is simply a number, picked at random. Ownership and control over the private key is the root of user control over all funds associated with the corresponding bitcoin address. The private key is used to create signatures that are required to spend bitcoins by proving ownership of funds used in a transaction. The private key must remain secret at all times, as revealing it to a third party is equivalent to giving them control over the bitcoins secured by that key.The private key must also be backed up and protected from accidental loss, since if lost it cannot be recovered and the funds secured by it are forever lost too.
The first and most important step in generating keys is to find a secure source of entropy, or randomness. Creating a bitcoin key is essentially the same as “Pick a number between 1 and 2^256“. The exact method you use to pick that number does not matter as long as it Is not predictable or repeatable.Bitcoin software uses the underlying operating system’s random number generators to produce 256 bits of entropy (randomness). Usually, the OS random number generator is initialized by a human source of randomness, which is why you may be asked to wiggle your mouse around for a few seconds. For the truly paranoid, nothing beats dice, pencil and paper.
All Bitcoin private keys is simply an integer between number 1 and 115792089237316195423570985008687907852837564279074904382605163141518161494337 or HEX: from 1 to 0xfffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141. The integer range of valid private keys is governed by the secp256k1 ECDSA standard used by Bitcoin.We just generate a range of these integers in sequence, divide into pages and show on each page. We can't store it and we have not saved database, because it should be biggest base on the world.You can find Private key in WIF (Wallet Import/Export Format) and compressed key. Bitcoin addresses in compressed/ uncompressed formats, SegWit (P2SH-P2WPKH) and native Segwit (P2WPKH) addesses start bc1, Pay to script hash (P2SH) starting with 3; legacy Bitcoin Cash addresses and new format.