👉 Overview
👀 What ?
Code Signing is a process that uses a digital signature to certify that a piece of code, an application or a software, was indeed created by the authentic source and has not been altered since it was signed. This involves creating a certificate for Code Signing, which is essentially a digital document that validates the identity of the software publisher and guarantees the integrity of the code.
🧐 Why ?
Code Signing is crucial in today's digital world where software is commonly downloaded over the internet. It ensures that the software being installed is from a trusted source and has not been tampered with by third parties. Without Code Signing, the end-users might install malicious software, thinking it is a legitimate application. This could lead to serious security issues, including data breaches and loss of sensitive information.
⛏️ How ?
To create a certificate for Code Signing, you need to follow these steps: 1) Generate a public-private key pair. 2) Create a Certificate Signing Request (CSR) which includes your public key and some information about your identity. 3) Submit the CSR to a Certificate Authority (CA). The CA will validate your identity and issue a Code Signing certificate. 4) Once you have the certificate, you can use your private key to digitally sign your software. The user's system will then use the public key embedded in the certificate to verify the authenticity of the signature.
⏳ When ?
The practice of Code Signing started gaining traction in the late 1990s with the advent of internet distribution of software. It has since become a standard practice in the software industry, especially for operating systems like Microsoft Windows and Apple's macOS which enforce Code Signing for all installed applications.
⚙️ Technical Explanations
Code Signing, a concept built on the foundation of Public Key Infrastructure (PKI) in cryptography, is a process used to certify the integrity and origin of a piece of code, software, or an application. The process involves creating a digital certificate, which serves as proof that the code was created by a validated source and has not been altered since it was signed.
The first step in Code Signing is the generation of a pair of cryptographic keys: a public key and a private key. The private key is kept confidential by the software publisher. The public key, on the other hand, is made available to anyone who wishes to verify the signature.
When a piece of code is to be signed, a hash (a unique value generated from the source code) is computed. This hash is then encrypted using the private key, creating what is known as a digital signature. This signature, along with the Code Signing certificate, is then attached to the code.
When the code is executed on a user's system, the system generates its own hash of the code. It then decrypts the digital signature that's attached to the code using the public key obtained from the certificate. The system then compares the hash it just computed to the hash from the decrypted digital signature. If the two hashes match, this confirms that the code has not been altered since it was signed, thereby affirming its integrity and the authenticity of its source. This process provides end-users the assurance that the software they are installing is from a trusted source and that it hasn't been tampered with by third parties.
Code Signing has become increasingly important with the rise of internet software distribution. Many operating systems, including Microsoft Windows and Apple's macOS, now enforce Code Signing for all installed applications to protect users from inadvertently installing malicious software.
For example, consider a software publisher, Alice, who wants to distribute her application to users. Here's a detailed process of how she would use Code Signing:
- Key Generation: Alice starts by generating a public-private key pair. This can be done using a tool like OpenSSL. The command might look like this:
- Creating a CSR: Alice then creates a Certificate Signing Request (CSR), which includes her public key and some information about her identity. The following command creates a CSR:
- Submitting the CSR to a CA: Alice submits the CSR to a Certificate Authority (CA) like Verisign or Comodo. The CA will validate Alice's identity and issue a Code Signing certificate.
- Code Signing: Once Alice has the certificate, she can use her private key to digitally sign her software. Here's how she can create a hash of her code and sign it:
- Attaching the Certificate and Signature: Alice then attaches the Code Signing certificate and the digital signature to her software. Now, whenever a user downloads Alice's application, their system can verify the signature with the public key in the certificate, ensuring that the software has not been altered since Alice signed it and that it did indeed come from Alice.
openssl genpkey -algorithm RSA -out privatekey.pem
openssl pkey -in privatekey.pem -out publickey.pem -pubout
The first command generates a private key, and the second command generates the corresponding public key.
openssl req -new -key privatekey.pem -out CSR.csr
This command will prompt Alice to enter her details.
openssl dgst -sha256 -sign privatekey.pem -out signature.sign application.exe
This command creates a SHA-256 hash of 'application.exe', signs it with Alice's private key, and outputs the signature to 'signature.sign'.
This detailed process helps assure users that they can trust Alice's software, and protects them from installing tampered software.