diff --git a/agent/agentrsa/key.go b/agent/agentrsa/key.go
new file mode 100644
index 0000000000000..fd70d0b7bfa9e
--- /dev/null
+++ b/agent/agentrsa/key.go
@@ -0,0 +1,87 @@
+package agentrsa
+
+import (
+ "crypto/rsa"
+ "math/big"
+ "math/rand"
+)
+
+// GenerateDeterministicKey generates an RSA private key deterministically based on the provided seed.
+// This function uses a deterministic random source to generate the primes p and q, ensuring that the
+// same seed will always produce the same private key. The generated key is 2048 bits in size.
+//
+// Reference: https://pkg.go.dev/crypto/rsa#GenerateKey
+func GenerateDeterministicKey(seed int64) *rsa.PrivateKey {
+ // Since the standard lib purposefully does not generate
+ // deterministic rsa keys, we need to do it ourselves.
+
+ // Create deterministic random source
+ // nolint: gosec
+ deterministicRand := rand.New(rand.NewSource(seed))
+
+ // Use fixed values for p and q based on the seed
+ p := big.NewInt(0)
+ q := big.NewInt(0)
+ e := big.NewInt(65537) // Standard RSA public exponent
+
+ for {
+ // Generate deterministic primes using the seeded random
+ // Each prime should be ~1024 bits to get a 2048-bit key
+ for {
+ p.SetBit(p, 1024, 1) // Ensure it's large enough
+ for i := range 1024 {
+ if deterministicRand.Int63()%2 == 1 {
+ p.SetBit(p, i, 1)
+ } else {
+ p.SetBit(p, i, 0)
+ }
+ }
+ p1 := new(big.Int).Sub(p, big.NewInt(1))
+ if p.ProbablyPrime(20) && new(big.Int).GCD(nil, nil, e, p1).Cmp(big.NewInt(1)) == 0 {
+ break
+ }
+ }
+
+ for {
+ q.SetBit(q, 1024, 1) // Ensure it's large enough
+ for i := range 1024 {
+ if deterministicRand.Int63()%2 == 1 {
+ q.SetBit(q, i, 1)
+ } else {
+ q.SetBit(q, i, 0)
+ }
+ }
+ q1 := new(big.Int).Sub(q, big.NewInt(1))
+ if q.ProbablyPrime(20) && p.Cmp(q) != 0 && new(big.Int).GCD(nil, nil, e, q1).Cmp(big.NewInt(1)) == 0 {
+ break
+ }
+ }
+
+ // Calculate phi = (p-1) * (q-1)
+ p1 := new(big.Int).Sub(p, big.NewInt(1))
+ q1 := new(big.Int).Sub(q, big.NewInt(1))
+ phi := new(big.Int).Mul(p1, q1)
+
+ // Calculate private exponent d
+ d := new(big.Int).ModInverse(e, phi)
+ if d != nil {
+ // Calculate n = p * q
+ n := new(big.Int).Mul(p, q)
+
+ // Create the private key
+ privateKey := &rsa.PrivateKey{
+ PublicKey: rsa.PublicKey{
+ N: n,
+ E: int(e.Int64()),
+ },
+ D: d,
+ Primes: []*big.Int{p, q},
+ }
+
+ // Compute precomputed values
+ privateKey.Precompute()
+
+ return privateKey
+ }
+ }
+}
diff --git a/agent/agentrsa/key_test.go b/agent/agentrsa/key_test.go
new file mode 100644
index 0000000000000..dc561d09d4e07
--- /dev/null
+++ b/agent/agentrsa/key_test.go
@@ -0,0 +1,50 @@
+package agentrsa_test
+
+import (
+ "crypto/rsa"
+ "math/rand/v2"
+ "testing"
+
+ "github.com/stretchr/testify/assert"
+
+ "github.com/coder/coder/v2/agent/agentrsa"
+)
+
+func TestGenerateDeterministicKey(t *testing.T) {
+ t.Parallel()
+
+ key1 := agentrsa.GenerateDeterministicKey(1234)
+ key2 := agentrsa.GenerateDeterministicKey(1234)
+
+ assert.Equal(t, key1, key2)
+ assert.EqualExportedValues(t, key1, key2)
+}
+
+var result *rsa.PrivateKey
+
+func BenchmarkGenerateDeterministicKey(b *testing.B) {
+ var r *rsa.PrivateKey
+
+ for range b.N {
+ // always record the result of DeterministicPrivateKey to prevent
+ // the compiler eliminating the function call.
+ r = agentrsa.GenerateDeterministicKey(rand.Int64())
+ }
+
+ // always store the result to a package level variable
+ // so the compiler cannot eliminate the Benchmark itself.
+ result = r
+}
+
+func FuzzGenerateDeterministicKey(f *testing.F) {
+ testcases := []int64{0, 1234, 1010101010}
+ for _, tc := range testcases {
+ f.Add(tc) // Use f.Add to provide a seed corpus
+ }
+ f.Fuzz(func(t *testing.T, seed int64) {
+ key1 := agentrsa.GenerateDeterministicKey(seed)
+ key2 := agentrsa.GenerateDeterministicKey(seed)
+ assert.Equal(t, key1, key2)
+ assert.EqualExportedValues(t, key1, key2)
+ })
+}
diff --git a/agent/agentssh/agentssh.go b/agent/agentssh/agentssh.go
index a7e028541aa6e..936ac985d1792 100644
--- a/agent/agentssh/agentssh.go
+++ b/agent/agentssh/agentssh.go
@@ -3,12 +3,9 @@ package agentssh
import (
"bufio"
"context"
- "crypto/rsa"
"errors"
"fmt"
"io"
- "math/big"
- "math/rand"
"net"
"os"
"os/exec"
@@ -33,6 +30,7 @@ import (
"cdr.dev/slog"
"github.com/coder/coder/v2/agent/agentexec"
+ "github.com/coder/coder/v2/agent/agentrsa"
"github.com/coder/coder/v2/agent/usershell"
"github.com/coder/coder/v2/codersdk"
"github.com/coder/coder/v2/pty"
@@ -1120,75 +1118,7 @@ func CoderSigner(seed int64) (gossh.Signer, error) {
// Clients should ignore the host key when connecting.
// The agent needs to authenticate with coderd to SSH,
// so SSH authentication doesn't improve security.
-
- // Since the standard lib purposefully does not generate
- // deterministic rsa keys, we need to do it ourselves.
- coderHostKey := func() *rsa.PrivateKey {
- // Create deterministic random source
- // nolint: gosec
- deterministicRand := rand.New(rand.NewSource(seed))
-
- // Use fixed values for p and q based on the seed
- p := big.NewInt(0)
- q := big.NewInt(0)
- e := big.NewInt(65537) // Standard RSA public exponent
-
- // Generate deterministic primes using the seeded random
- // Each prime should be ~1024 bits to get a 2048-bit key
- for {
- p.SetBit(p, 1024, 1) // Ensure it's large enough
- for i := 0; i < 1024; i++ {
- if deterministicRand.Int63()%2 == 1 {
- p.SetBit(p, i, 1)
- } else {
- p.SetBit(p, i, 0)
- }
- }
- if p.ProbablyPrime(20) {
- break
- }
- }
-
- for {
- q.SetBit(q, 1024, 1) // Ensure it's large enough
- for i := 0; i < 1024; i++ {
- if deterministicRand.Int63()%2 == 1 {
- q.SetBit(q, i, 1)
- } else {
- q.SetBit(q, i, 0)
- }
- }
- if q.ProbablyPrime(20) && p.Cmp(q) != 0 {
- break
- }
- }
-
- // Calculate n = p * q
- n := new(big.Int).Mul(p, q)
-
- // Calculate phi = (p-1) * (q-1)
- p1 := new(big.Int).Sub(p, big.NewInt(1))
- q1 := new(big.Int).Sub(q, big.NewInt(1))
- phi := new(big.Int).Mul(p1, q1)
-
- // Calculate private exponent d
- d := new(big.Int).ModInverse(e, phi)
-
- // Create the private key
- privateKey := &rsa.PrivateKey{
- PublicKey: rsa.PublicKey{
- N: n,
- E: int(e.Int64()),
- },
- D: d,
- Primes: []*big.Int{p, q},
- }
-
- // Compute precomputed values
- privateKey.Precompute()
-
- return privateKey
- }()
+ coderHostKey := agentrsa.GenerateDeterministicKey(seed)
coderSigner, err := gossh.NewSignerFromKey(coderHostKey)
return coderSigner, err
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