#ssh  #dev 

RSA vs ED25519

TL;DR:

  • Use ED25519 (if supported)
  • Unless you’re targeting legacy systems, prefer ed25519 — it’s more modern, secure, and faster.
  • ED25519: Modern, compact, faster — recommended
  • RSA: Widely compatible, older, heavier — use if needed for legacy support

Detailed Comparison

Feature RSA ED25519
🔐 Algorithm Type Asymmetric, based on factoring Elliptic Curve Cryptography (ECC)
🔒 Security Good (4096-bit recommended) Stronger at smaller size
📏 Key Size 2048 / 3072 / 4096 bits 256 bits (only)
🚀 Speed Slower (especially for signing) Faster for both signing and verifying
⏳ Age Older, well-tested Newer (since OpenSSH 6.5, 2014)
🔧 Config Flexibility More tunable options Simpler (fixed size)
📉 Size (private key) Larger Smaller
👴 Compatibility Universally supported Requires OpenSSH ≥ 6.5
🧱 Quantum Resistance Not resistant Also not resistant

When to Use Each

Use Case Recommended Key
Working with modern systems (GitHub, GitLab, SSH servers) ✅ ED25519
Need compatibility with older servers, VPNs, or enterprise systems ✅ RSA 4096-bit

How to Generate (Examples)

# ED25519
ssh-keygen -t ed25519 -C "[email protected]"

# RSA (4096-bit)
ssh-keygen -t rsa -b 4096 -C "[email protected]"

Managing multiple SSH keys for both GitHub and Bitbucket, each with personal and work accounts

GitHub identifies SSH keys by the email/username attached to the key, so you need to configure them properly

1. Generate SSH Keys

# GitHub Personal
ssh-keygen -t ed25519 -C "personal-github" -f ~/.ssh/id_ed25519_github_personal

# GitHub Work
ssh-keygen -t ed25519 -C "vgc-github" -f ~/.ssh/id_ed25519_github_vgc
ssh-keygen -t ed25519 -C "td2c-github" -f ~/.ssh/id_ed25519_github_td2c
ssh-keygen -t ed25519 -C "ap-github" -f ~/.ssh/id_ed25519_github_ap
ssh-keygen -t ed25519 -C "rw-bit" -f ~/.ssh/id_ed25519_bit_rw

# Bitbucket Personal
ssh-keygen -t ed25519 -C "personal-bitbucket" -f ~/.ssh/id_ed25519_bitbucket_personal

# Bitbucket Work
ssh-keygen -t ed25519 -C "work-bitbucket" -f ~/.ssh/id_ed25519_bitbucket_work

2. Add Public Keys to Respective Accounts

  • Upload these .pub files to:
    • GitHub → Settings → SSH & GPG keys
    • Bitbucket → Personal Settings → SSH keys
vim ~/.ssh/id_ed25519_bit_rw.pub

3. Configure ~/.ssh/config

# GitHub Personal
Host github-ap
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_ed25519_github_ap

# GitHub Work
Host github-vgc
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_ed25519_github_vgc

# GitHub Work2
Host github-td2c
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_ed25519_github_td2c

# Bitbucket Personal
Host bitbucket-personal
  HostName bitbucket.org
  User git
  IdentityFile ~/.ssh/id_ed25519_bitbucket_personal


# Bitbucket Work3
Host bitbucket-rw
  HostName bitbucket.org
  User git
  IdentityFile ~/.ssh/id_ed25519_bit_rw

Clone Repositories Using Aliases

git clone git@github-personal:username/repo.git

git clone git@github-vgc:org/repo.git
git clone git@github-td2c:org/repo.git

git clone git@bitbucket-personal:username/repo.git

git clone git@bitbucket-rw:org/repo.git

5. Set Per-Repo Identity

git config user.name "Your Work/Personal Name"
git config user.email "[email protected]"