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Encryption. Public-Key, Identity-Based, Attribute-Based. I. Public key encryption and security concepts. Eve. Use encryption to prevent eavesdropping and achieve confidentiality. Public key encryption. Bob generates pair of public key pk B and secret key sk B
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Encryption Public-Key, Identity-Based, Attribute-Based
I. Public keyencryptionandsecurityconcepts Eve Use encryption to prevent eavesdropping and achieve confidentiality.
Public keyencryption • Bob • generates pair of public key pkB and secret key skB • makes pkB public • decrypts with skB • Alice • encrypts messagem with pkB • sends encrypted message/ciphertextc
Security concepts • Security concepts must specify • goals of adversary • resources of adversary • additional information available to adversary. • adversaries should learn almost nothing about plaintext given a ciphertext • adversaries will be probabilistic polynomial time algorithms. • adversaries known complete specifications of encryption schemes (Kerckhoff’s principle) • additional information formalized with chosen plaintext and chosen ciphertext attacks
CCA security Observation CPA security does not imply CCA security.
PKC andreality Certification Authority (CA)
Certificatesandcertificationauthorities • require significant organizational and technical overhead • require complex data management • their complexity can become a threat to security
Public key vs. identity-basedencryption • PKE requires special pairs of keys, not all bit strings can be public keys • in IBE every bit string or identity can be public key • identities can already be certified, e.g. passport numbers • may simplify necessary infrastructure • IBE introduced in 1984 by A. Shamir • first fully functional realization in 2001 by Boneh, Franklin • can be generalized to attribute-based encryption
Identity-basedenryption Private Key Generator
Identity-basedenryption Private Key Generator
Security concepts • Security concepts must specify • goals of adversary • resources of adversary • additional information available to adversary. • adversaries should learn almost nothing about plaintext given a ciphertext • adversaries will be probabilistic polynomial time algorithms. • adversaries known complete specifications of encryption schemes (Kerckhoff’s principle) • additional information formalized with chosen plaintext and chosen ciphertext attacks
IBE security – additional requirements • adversaries should learn almost nothing about plaintext given a ciphertext • adversaries will be probabilistic polynomial time algorithms. • adversaries known complete specifications of encryption schemes (Kerckhoff’s principle) • additional information formalized with chosen plaintext and chosen ciphertext attacks • adversary may know private keys to many identities Challenge Exponentially (in n) many private keys depend on master secret msk of polynomial (in n) length.
Power of PKG • PKG is • very powerful • attractive target for attacks • Possible solutions • secure protocols • distributed realization Private Key Generator
PKG via secureprotocols Private Key Generator
Boneh-Franklin IBE andpairings • uses one basic primitive – bilinear pairings • concrete realization with groups on elliptic curves • examples are Weil, Tate, Eta, Ate pairing • but can be described with generic pairings • share this feature with most techniques in IBC