1. 1 Pertemuan 12 E-mail Security Matakuliah: H0242 / Keamanan Jaringan Tahun: 2006 Versi: 1

2. 2 Learning Outcomes Pada akhir pertemuan ini, diharapkan mahasiswa akan mampu : –Mahasiswa dapat menggunakan e-mail security

3. 3 Outline Materi Konsep kerja e-mail Layanan keamanan pada e-mail PGP S / MIME

4. 4 Email Security E-mail is one of the most widely used and regarded network services Currently message contents are not secure, missing the following security characteristics –Confidentiality Protection from disclosure –Authentication Of sender of message –Message integrity Protection from modification –Non-repudiation of origin Protection from denial by sender

5. 5 Pretty Good Privacy (PGP) Widely used de facto secure email Selected best available crypto algorithms to use, integrated into a single program originally free, now have commercial versions available Wide range of applicability Not developed or controlled by governmental or standards organizations

6. 6 PGP Operational Description Consist of five services: –Authentication –Confidentiality –Compression –E-mail compatibility –Segmentation

7. 7 Confidentiality & Authentication Uses both services on same message –Create signature & attach to message –Encrypt both message & signature –Attach RSA encrypted session key

8. 8 Authentication 1.Sender creates a message 2.SHA-1 used to generate 160-bit hash code of message 3.Hash code is encrypted with RSA using the sender's private key, and result is attached to message 4.Receiver uses RSA or DSS with sender's public key to decrypt and recover hash code 5.Receiver generates new hash code for message and compares with decrypted hash code, if match, message is accepted as authentic

9. 9 Confidentiality 1.Sender generates message and random 128-bit number to be used as session key for this message only 2.Message is encrypted, using CAST-128 / IDEA/3DES with session key 3.Session key is encrypted using RSA with recipient's public key, then attached to message 4.Receiver uses RSA with its private key to decrypt and recover session key 5.Session key is used to decrypt message

10. 10 Compression By default PGP compresses message after signing but before encrypting –Store uncompressed message & signature for later verification because compression is non deterministic Uses ZIP compression algorithm

11. 11 Email Compatibility When using PGP will have binary data to send (encrypted message, etc);however, email was designed only for text PGP must encode raw binary data into printable ASCII characters, uses radix-64 algorithm –maps 3 bytes to 4 printable chars –also appends a CRC PGP also segments messages if too big

12. 12 E-mail Compatibility The scheme used is radix-64 conversion The use of radix-64 expands the message by 33%.

13. 13 Segmentation & Reassembly Often restricted to a maximum message length of 50,000 octets. Longer messages must be broken up into segments. PGP automatically subdivides a message that is to large. The receiver strip of all e-mail headers and reassemble the block.

14. 14 Sumary of PGP Services

15. 15 SMTP SMTP (RFC 822) Limitations –Can not transmit, or has a problem with: Executable files, or other binary files (JPG) National language characters (non-ASCII) Messages over a certain size ASCII to EBCDIC translation problems Lines longer than a certain length (72 to 254 characters)

16. 16 S/MIME Secure/Multipurpose Internet Mail Extensions Security enhancement to MIME email –MIME provided support for varying content types and multi-part messages with encoding of binary data to textual form –S/MIME added security enhancements Support in various modern mail agents: MS Outlook, Netscape, etc Will probably emerge as the industry standard, whereas PGP for personal e-mail security

17. 17 Header fields in MIME MIME-Version: –Must be 1.0 (RFC 2045, RFC 2046) Content-Type: –More types being added by developers Content-Transfer-Encoding: –How message has been encoded (radix-64) Content-ID: –Unique identifying character string. Content Description: –Needed when content is not readable text

18. 18 S/MIME Functions Enveloped Data: –Encrypted content and encrypted session keys for recipients. Signed Data: –Message Digest encrypted with private key of signer Clear-Signed Data: –Signed but not encrypted. Signed and Enveloped Data: –Various orderings for encrypting and signing.

19. 19 Algorithms Used Message Digesting: –SHA-1 and MDS Digital Signatures: –DSS Secret-Key Encryption: –Triple-DES –RC2/40 (exportable) Public-Private Key Encryption: –RSA with key sizes of 512 and 1024 bits –Diffie-Hellman (for session keys).

20. 20 User Agent Role S/MIME uses Public-Key Certificates - X.509 version 3 signed by Certification Authority Functions: –Key Generation Diffie-Hellman, DSS, and RSA key-pairs. –Registration Public keys must be registered with X.509 CA. –Certificate Storage Local (as in browser application) for different services. –Signed and Enveloped Data Various orderings for encrypting and signing.

21. 21 Cryptographic Algorithms Hash functions: –SHA-1 & MD5 Digital signatures: –DSS & RSA Session key encryption: –ElGamal & RSA Message encryption: –Triple-DES, RC2/40 and others Have a procedure to decide which algorithms to use

22. 22 Certificate Processing S/MIME uses X.509 v3 certificates Managed using a hybrid of a strict X.509 CA hierarchy & PGP’s web of trust Each client has a list of trusted CA’s certificates and own public/private key pairs & certificates Certificates must be signed by trusted CA’s