8. Hash algorithms
• Generate a constant size fingerprint whatever
data in entry
• It’s hard to find the message from the given hash
(First Preimage Resistance)
• It’s hard to modify a message without hash
being changed (Second Preimage Resistance)
• It’s hard to find two different messages with the
same hash (Resistance to Collisions)
• Very fast calculation
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9. Cryptographic
Hash algorithms
• Generate a constant size fingerprint whatever
data in entry
infeasible
• It’s hard to find the message from the given hash
(First Preimage Resistance)
infeasible
• It’s hard to modify a message without hash
being changed (Second Preimage Resistance)
infeasible
• It’s hard to find two different messages with the
same hash (Resistance to Collisions)
• Very fast calculation
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11. Hash functions
Integrity checking : Fingerprint or checksum
hash()
File 415a15b606eff4d4ba97ef64ecd2e598
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12. Hash functions
Integrity checking : Fingerprint or checksum
hash()
File 415a15b606eff4d4ba97ef64ecd2e598
Very low probability of collision !
Hard to change file without changing hash !
Fast algorithm !
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14. Hash functions
Password encryption :
hash()
password 415a15b606eff4d4ba97ef64ecd2e598
Hard to calculate password from the
hash !
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15. Hash functions
Remember me tokens :
username + expiration date + hash(password)
hash()
415a15b606eff4d4ba97ef64ecd2e598
Remember me token = hash(...) + username + expiration date
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16. Password hashing leaks
• Brute force
• Dictionary
• Rainbow table
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17. Password hashing leaks
• Brute force
• Dictionary
• Rainbow table
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18. Salted hash functions
Salted hash password :
hash()
salt + password hash(salt+password)
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19. Salted hash functions
Salted hash password :
hash()
salt + password hash(salt+password)
secret and / or
user dependent
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20. Salted hash functions
Salted hash password :
hash()
salt + password hash(salt+password)
secret and / or
user dependent
Prevents from dictionary and
rainbow table attacks !
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21. Hash function algorithms
• Message Digest 5
• 128 bits fingerprint size
• Secured Hash Algorithm
• many version (SHA1, SHA256 ...)
• 160 to 512 bits fingerprint size
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22. Hash function algorithms
• Message Digest 5 @deprecated
• 128 bits fingerprint size
• Secured Hash Algorithm
• many version (SHA1, SHA256 ...)
• 160 to 512 bits fingerprint size
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23. Symmetric algorithms
• Shared secret key algorithm
• Same key used to cipher and decipher
• Fast algorithm
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24. Popular symmetric
algorithms
• Advanced Encryption Standard
• Blowfish
• Digital Encryption Standard and 3DES
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25. Popular symmetric
algorithms
• Advanced Encryption Standard
• Blowfish
• Digital Encryption Standard and 3DES
@deprecated
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46. Digital signature
Unchanged hash means
unaltered message
compare hash("hello.")
with :
dsa("er2f@!e..", PuK.alice)
Bob checks signature
with Alice public key
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57. Public Key Infrastructure !
• Public key certificate
• Certificate management
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58. Public key certificates
• Binds public key with Identity
• Can be used to :
• authenticate a user
• cipher data (email, communications ...)
• prove identity (SSL)
• signing a document
• signing a certificate (CA certificate)
• ...
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59. Public key
certificate
anatomy
(TLS certificate)
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61. Public key certificate anatomy -
Issuer
Issuer Distinguished Name
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62. Public key certificate anatomy -
Issuer
Issuer Distinguished Name
Issuer ≠ Subject :
• Not a CA certificate
• Not a self signed certificate
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69. Public key certificate anatomy -
Extensions
Not a CA certificate
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70. Public key certificate anatomy -
Extensions
Not a CA certificate
Revocation List
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71. Public key certificate anatomy -
Extensions
Not a CA certificate
Revocation List
Certificate usage (TLS)
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72. Public key certificate anatomy -
Extensions
Not a CA certificate
Revocation List
Certificate usage (TLS)
Issuer CA certificate location
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74. Public key certificate anatomy -
Certificate signature
The certificate SHA1 fingerprint is signed with Issuer
private key
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75. Certificate fingerprint
signature
• Self signed or signed by CA
• Prevents certificate corruption
• CA signing proves identity if the CA is
trusted
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86. Certificate management
CR is signed with Manage CRL or OCSP
CA private key
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87. Certificate management
CR is signed with Manage CRL or OCSP
CA private key
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88. Certificate management
CR is signed with Manage CRL or OCSP
CA private key
Check Bob certificate
with CA certificate
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89. Certificate management
CR is signed with Manage CRL or OCSP
CA private key
Check Bob certificate
with CA certificate
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90. Certificate management
CR is signed with Manage CRL or OCSP
CA private key
Check Bob
certificate validity
Check Bob certificate
with CA certificate
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91. Private key storage
• Password protected PKCS12 file
• Cryptographic token :
• password protected
• key pair generation (not possible to take the
private key out)
• process asymmetric algorithms (RSA, DSA,
Diffie-Hellman ...)
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92. Private key storage
• Password protected PKCS12 file
• Cryptographic token :
• password protected
• key pair generation (not possible to take the
private key out)
• process asymmetric algorithms (RSA, DSA,
Diffie-Hellman ...)
Two Factors Authentication :
protect with something you know and something
you have
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93. Certificate revocation
• Two protocols :
• Certificate Revocation List
• Online Certificate Status Protocol
• CRL provides a full certificates revocation
list
• OCSP is request/response protocol
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94. One Time Password
• Token and password (PIN) based
authentication system
• Token uses a clock and a secret algorithm
to generate a OTP
• OTP server use the same algorithm to
validate the OTP
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95. Conclusion
• What’s going on if you loose your
ciphering private key (or PKCS12
password) ?
• Are the Registration Authority validation
process safe ?
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