• Photo Crypto Auth
  • literature
    • P3: Toward Privacy-Preserving Photo Sharing, Moo-Ryong Ra, Ramesh Govindan, Antonio Ortega, NSDI 13
    • Mitigating Image-based Misinformation Campaigns, Calvin Ardi, Harsha V. Madhyastha
  • C2PA
  • idea

Photo Crypto Auth

• cameras will sign photo cryptographically
• influencer have posted genuine photo but for irrelevant event
• may build system to authenticate photo

problem:

• ~~what about photo without signature?~~don’t care

steps:

1. What in photo from C2PA camera?
2. Post-processing on social media site preserve signature?
3. Extract info from posts’ text

literature

P3: Toward Privacy-Preserving Photo Sharing, Moo-Ryong Ra, Ramesh Govindan, Antonio Ortega, NSDI 13

split photo into public and private part, encrypt private part

Mitigating Image-based Misinformation Campaigns, Calvin Ardi, Harsha V. Madhyastha

proposal: compare photo crypto metadata time+location w/ social media post text before manipulative post go viral. good for news. need to balance privacy

C2PA

• nesting: manifest (metadata) > claim (wrapper) > assertion (statement)
• claim generator: create & sign claim
• manifest consumer, e.g., C2PA validator
• public key encryption (ECDSA/EdDSA/RSA) to sign claim; SHA-2 hash for hard binding of manifest & content
• modifying image invalidate previous signature, need new one: 10.3.3.2. Multiple Claims | Content Credentials : C2PA Technical Specification :: C2PA Specifications
  • PhotoShop seem to keep private key on cloud, see Content credentials in Photoshop
• attack: see Threat | C2PA Security Considerations :: C2PA Specifications onward
  • steal private key/ trick claim generator/ make key → penetrate
  • security guidance: “best practice”
    • hardware security module (HSM); revoke
  • Canon signing key leak from 2010: Analyst Finds Flaws in Canon Image Verification System | PCWorld
  • no transitive trust; probably whack-a-mole security patching
  • could add any author name during editing: blog
• how actually done
  • check out C2PA editing software
    • few options.
    • Adobe is biggest
    • PixelStream seems vaporware. blog from CAI: Community story: Pixelstream. but dead GitHub and website
    • Photo Mechanic is for camera
    • Cloudinary is for content delivery
      • Try after sign up: only preserve existing, do not add new; need to join beta program
    • Microsoft Designer is not advertised
  • check out C2PA image
    • generated cat picture signed later
  • Check out C2PA SDK
• Note down potential issues
  • Removing metadata rids hard binding. Soft binding improvements?
  • Camera private key leak
  • Editing software lose track
  • Taking photo of photo
    • ❗Literatures? Difference between photo of photo and photo
      • Bad search term. Only found paper on distinguishing manipulated photo.
  • PKI: long term verification support?
    • ❗Literatures? Trusting signed document long term
      • Check out signed digest standard
• use case: prove my photo is real
  • news, social media
  • legal, forensic
  • artwork
  • research proof

idea

• get something then reach out to C2PA people
• RGBD camera to combat taking photo of photo