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IKE Transform Set Enumeration

3 min read Mar 30, 2026

An IKE gateway accepts connections only from peers that propose a matching set of cryptographic parameters — the transform set. Enumerating every accepted combination tells you the full attack surface: which weak algorithms are permitted, whether PSK authentication is accepted, and what is needed to establish a valid negotiation for exploitation.

The initial service detection probe returns one accepted transform. This page covers systematically extracting all of them.

ike-scan with a Single Transform

ike-scan sends a proposal with one transform set per probe. Specify the components manually:

┌──(kali㉿kali)-[~]
└─$ sudo ike-scan --trans=5,2,1,2 $TARGET_IP
Explain command
--trans=5,2,1,2 Specifies IKE transform: enc=3DES, hash=SHA1, auth=preshared, DH group=2
$TARGET_IP Target IP address variable for the IKE scan

The four numbers map to: encryption,hash,auth,dh-group

Common values:

Field

Value

Meaning

Encryption

1

DES

Encryption

5

3DES

Encryption

7

AES-128

Hash

1

MD5

Hash

2

SHA1

Hash

4

SHA2-256

Auth

1

PSK

Auth

3

RSA signatures

DH Group

1

modp768

DH Group

2

modp1024

DH Group

5

modp1536

DH Group

14

modp2048

A Handshake returned response means the gateway accepted that transform. A Notify or no response means it was rejected.

Scripted Enumeration with ikeforce

ikeforce automates the transform set sweep, testing all common combinations and reporting which ones the gateway accepts:

┌──(kali㉿kali)-[~]
└─$ python2 ikeforce.py $TARGET_IP -e 
[*] Scanning with: Enc=DES, Hash=MD5, Auth=PSK, DH=1
[*] Scanning with: Enc=DES, Hash=SHA1, Auth=PSK, DH=1
[+] Found accepted transform: Enc=3DES, Hash=SHA1, Auth=PSK, DH=2
[+] Found accepted transform: Enc=AES, Hash=SHA2-256, Auth=PSK, DH=14
Explain command
$TARGET_IP Target IP address to probe for IKE services.
-e Enable enumeration mode to identify valid group names/IDs.

Each [+] line is a working combination. Record all of them — the weakest accepted transform matters most for the vulnerability assessment.

Manual Sweep with ike-scan

If ikeforce is not available, sweep manually with a loop. Write a short list of transforms to test and iterate:

for trans in "1,1,1,1" "1,2,1,1" "5,1,1,2" "5,2,1,2" "7,1,1,2" "7,2,1,2" "7,4,1,14"; do
  result=$(sudo ike-scan --trans=$trans $TARGET_IP 2>/dev/null)
  if echo "$result" | grep -q "Handshake returned"; then
    echo "ACCEPTED: $trans"
  fi
done

IKEv2 Transform Enumeration

IKEv2 uses a slightly different structure. ike-scan supports IKEv2 probes with the --ikev2 flag:

┌──(kali㉿kali)-[~]
└─$ sudo ike-scan --ikev2 --trans=12,2,1,14 $TARGET_IP
Explain command
--ikev2 Use IKEv2 (Internet Key Exchange version 2) protocol for scanning.
--trans=12,2,1,14 Specify transform attributes: encr=AES(12), hash=SHA1(2), auth=PSK(1), dh=2048(14).
$TARGET_IP Placeholder for the target host IP address to scan.

IKEv2 encryption attribute values differ from IKEv1. The important thing to confirm with IKEv2 is whether weak DH groups (1, 2, 5) are accepted alongside modern ones — a gateway that accepts both creates downgrade opportunities.

What to Record

After sweeping, document:

  • Every accepted transform combination

  • Whether PSK (Auth=1) is accepted — required for offline cracking attacks

  • The weakest accepted cipher — DES and 3DES are broken, MD5 is weak

  • The weakest accepted DH group — groups 1 and 2 are considered broken

  • Whether Aggressive Mode is accepted — covered in IKEv1 Aggressive Mode Enabled

Any accepted weak transforms feed directly into Weak IKE Transform Sets.

References