Rsaes-pkcs1-v1_5

As explained in Hacking Cryptography

PKCS #1 v1.5 is an RSA encoding standard that defines formatting and randomized padding for encryption and related operations.

PKCS #1 v1.5 protects RSA signatures by requiring a rigid, recognizable encoding before the RSA operation. Formatting turns a random RSA result into a useful signature only when every required field is valid. section 9.6.1 section 9.7

A signature’s recovered cleartext follows this structure:

• Begin with the two bytes 00 01. section 9.6.1
• Fill the padding region entirely with FF bytes, then add a 00 separator. section 9.6.1 section 9.7
• Append an ASN.1 identifier for the hash algorithm and the computed hash digest. section 9.6.1

Why validation must be exact

With a small public exponent such as e = 3, an attacker can construct values whose cube resembles a desired cleartext. Weak checks that accept incorrect padding can therefore enable a forged signature; requiring every padding byte to equal FF blocks this failure. section 9.7

Figure 9.9 PKCS#1 v1.5 formatting for input to RSA signatures: The padding area should be filled with FF bytes.

Inspect the byte-level signature layout, including the FF-filled padding area. section 9.6.1

How Hacking Cryptography covers it

How deep it goes

Defines the byte layout and traces cube-root forgery, emphasizing exact FF validation rather than general RSA theory.

Examples

Uses 00 01 headers, FF padding, ASN.1 hash identifiers, e = 3, cube roots, and forged signatures.

What it assumes

Assumes RSA signatures and hash digests, while explaining the required byte formatting and ASN.1 identifiers.

What you can do after

Diagnose/debug RSA signature verifiers by enforcing the complete PKCS #1 v1.5 structure and rejecting malformed padding.

How it connects

Connects RSA signatures with hash functions, ASN.1, public exponents, existential forgery, and Bleichenbacher attacks.

liveBookmanning.com

Read Hacking Cryptography on liveBook Get the book at manning.com

Also explained in

• 

  liveBookmanning.com
  Real-World CryptographyRSA PKCS#1 v1.5 is an RSA encryption and signature specification version whose encryption encoding uses legacy padding vulnerable to adaptive padding-oracle attacks.
• 

  liveBookmanning.com
  Software Security for DevelopersRSAES-PKCS1-v1_5 is an RSA encryption scheme that encodes messages using the PKCS #1 version 1.5 encryption encoding method.

Compare how 3 books explain rsaes-pkcs1-v1_5 →

Related concepts

• Bleichenbacher's e=3 forgery attackused by · Bleichenbacher's e=3 forgery attack is an RSA signature-forgery attack that exploits lax validation of PKCS #1 v1.5 signature padding when the public exponent is 3.
• signature forgery attackused by · A signature forgery attack produces a signature that a verifier accepts as authentic without authorization from the legitimate signer's private key.
• RSAkind of · RSA is a public-key cryptosystem based on the computational difficulty of factoring large composite integers and supporting encryption and digital signatures.
• paddingkind of · Padding is the addition of extra space, values, or data around or within a structure to satisfy size, alignment, layout, or processing requirements.
• rsa-oaepalternative to · RSA-OAEP is a randomized RSA encryption scheme that encodes plaintext with hash-based Optimal Asymmetric Encryption Padding before encryption.

This explainer was generated by Manning's knowledge graph from the text of Hacking Cryptography. The section links point to the parts of the book it draws on.