Henric Johnson 2
S/MIME
•Secure/Multipurpose Internet Mail Extension
• S/MIME will probably emerge as the industry standard.
• The protocol is an enhancement of the Multipurpose Internet Mail Extension
(MIME) protocol.
• It can send messages only in NVT 7-bit ASCII format.
• MIME is a supplementary protocol that allows non-ASCII data to be sent through
e-mail.
• MIME transforms non-ASCII data at the sender site to NVT ASCII data and delivers
it to the client MTA to be sent through the Internet.
4.
Henric Johnson 4
Headerfields in MIME
• MIME-Version: Must be “1.0”
• Content-Type: More types being added by developers (application/word)
• 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 (e.g.,mpeg)
7.
Henric Johnson 7
S/MIMEContent type
• S/MIME adds some new content types to include security services to
the MIME.
• . All new types include the parameter “application/pkcs7-mime,” in
which “pkcs” defines “Public Key Cryptography Specification.”
• Enveloped Data: Encrypted content and 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.or Digest Data content type.
13.
Henric Johnson 13
AlgorithmsUsed
• Message Digesting: SHA-1 and MDS
• Digital Signatures: DSS
• Secret-Key Encryption: Triple-DES, RC2/40
• Public-Private Key Encryption: RSA with key sizes of 512 and 1024
bits, and Diffie-Hellman (for session keys).
14.
Henric Johnson 14
Keymanagement
• The key management in S/MIME is a combination of key management used by
X.509 and PGP.
• S/MIME uses public-key certificates signed by the certificate authorities defined
by X.509.
• the user is responsible to maintain the web of trust to verify signatures as
defined by PGP.
