About

Blockchain-based certificates solve a critical problem in credential verification: forgery. A traditional PDF certificate can be duplicated and altered in minutes. This generator produces certificates that embed cryptographic metadata - a txHash derived from SHA-256 hashing of the certificate payload and a deterministic Ethereum-style wallet address for the recipient. The hash changes if a single character is modified, making tampering detectable. The tool uses the native Web Crypto API to compute real SHA-256 digests, not random strings.

Limitations apply. This tool generates certificates styled after blockchain records but does not broadcast transactions to the Ethereum mainnet or any testnet. The txHash and address are cryptographically valid hashes of your input data, not on-chain entries. For actual on-chain certification, you would need a smart contract deployment costing gas fees in ETH. Pro tip: save the generated hash alongside the certificate - anyone can re-hash the same inputs to verify authenticity offline.

Formulas

The certificate transaction hash is computed by concatenating all certificate fields into a single payload string, then applying SHA-256:

txHash = 0x ⋅ SHA256(recipient + title + issuer + date + description)

The recipient Ethereum-style address is derived by hashing only the recipient name and truncating to 20 bytes (40 hex characters):

address = 0x ⋅ SHA256(recipient)[0:40]

The simulated block number derives from the Unix timestamp of the issuance date divided by an average block time of 12 seconds, offset from the Ethereum genesis block:

blockNumber = timestamp − genesisTimestamp12

Where recipient is the full name string, title is the certificate title, issuer is the issuing organization, date is the ISO-8601 date string, and description is the achievement text. genesisTimestamp = 1438269973 (July 30, 2015 UTC).

Reference Data

Field	Format	Example	Purpose
Transaction Hash	0x + 64 hex chars	0x3a7f...	Unique certificate fingerprint
Recipient Address	0x + 40 hex chars	0x8B3c...	Deterministic identity from name
Block Number	Integer	19284756	Simulated block height from timestamp
Gas Used	Integer wei	21000	Standard ETH transfer gas
SHA-256 Digest Size	256 bits	32 bytes	Hash output length
Ethereum Address Length	20 bytes	40 hex chars	Wallet identifier size
Certificate Canvas Width	1200 px	-	High-res export
Certificate Canvas Height	850 px	-	Landscape A4 ratio
Collision Probability (SHA-256)	1 in 2¹²⁸	~3.4 × 10³⁸	Birthday attack threshold
Keccak-256 (real ETH)	256 bits	-	Actual Ethereum hash function
EIP-55 Checksum	Mixed-case hex	0x5aAe...	Address validation standard
Certificate Status: Valid	Boolean	TRUE	Hash matches payload
Certificate Status: Tampered	Boolean	FALSE	Hash mismatch detected
Network	String	Mainnet / Sepolia	Display context
Standard Gas Price	20 Gwei	20 × 10⁹ wei	Typical transaction cost unit

Frequently Asked Questions

No. The generated transaction hashes and addresses are cryptographically valid SHA-256 digests computed locally in your browser using the Web Crypto API. They are not broadcast to any Ethereum network. To record a certificate on-chain, you would need to deploy a smart contract and pay gas fees in ETH. However, the hashes produced here are deterministic - re-entering the same data always yields the same hash, enabling offline verification.

The SHA-256 hash changes completely due to the avalanche effect. Even a one-bit change in the input produces a statistically independent 256-bit output. This means the transaction hash on the certificate will be entirely different, which is the core property that makes hash-based verification tamper-evident.

Keccak-256 (the actual hash function used by Ethereum for addresses and transaction IDs) is not natively available in the Web Crypto API, which only supports SHA-1, SHA-256, SHA-384, and SHA-512. Implementing Keccak-256 from scratch would add roughly 500 lines of code. SHA-256 provides identical security properties (256-bit output, collision resistance of 2 to the power of 128) and produces visually identical hex strings for certificate purposes.

Yes. Take the original input data (recipient name, title, issuer, date, description), concatenate them in the same order, compute SHA-256, and prefix with 0x. If the result matches the hash on the certificate, the data is authentic. Any standard SHA-256 tool (OpenSSL, Python hashlib, online calculators) can perform this verification.

The certificate renders at 1200 × 850 pixels on a Canvas element, which corresponds approximately to a landscape A4 aspect ratio at 96 DPI. The exported PNG file preserves this resolution. For print at 300 DPI, the image covers roughly 4 × 2.8 inches. For higher print quality, consider using the certificate data to populate a vector template in a dedicated design tool.

The address is the first 40 hexadecimal characters of the SHA-256 hash of the recipient's name, prefixed with 0x. This produces a 20-byte value consistent with the Ethereum address format (EIP-55 uses mixed-case checksumming which this tool does not apply, as the addresses are illustrative). The address is deterministic: the same name always produces the same address.