What exactly is the string that gets signed?

HTTPMethod + ':' + EndpointUrl + ':' + lowercase(hex(SHA-256(minify(body)))) + ':' + X-TIMESTAMP. The method is upper-cased, the body is minified JSON, and its SHA-256 is written as lowercase hex. Join the four parts with colons and sign that exact string.

Which key goes where?

Signing uses the private key of the sender. Verification uses the public key of the sender, not yours. For a notification you received, the sender is the payment provider, so paste the public key they published.

Why is the body minified before hashing?

The signature must not depend on cosmetic whitespace, so both sides agree to strip it first. JSON.stringify(JSON.parse(body)) removes the formatting and the receiver hashes the same compact form. If the body is not valid JSON it is hashed as typed.

Is this the same as SHA256withRSA in Java or Node?

Yes. Web Crypto's RSASSA-PKCS1-v1_5 with SHA-256 is exactly SHA256withRSA, so a signature made here verifies in Java, Node or any SNAP BI library, and the other way round.

Can I use a production private key here?

Technically yes, but do not. This is a public web page, so paste a test key, or press Generate key pair to create a throwaway 2048-bit pair and try the flow end to end.

SNAP BI Asymmetric Signature

Build the string to sign and sign or verify it with SHA256withRSA, the way Bank Indonesia's SNAP BI standard and Midtrans notifications do. Keys and data stay in your browser.

Action HTTP method Endpoint URL X-TIMESTAMP

Body

{"originalPartnerReferenceNo":"GP24043015193402809","originalReferenceNo":"A120240430081940S9vu8gSjaRID","merchantId":"G099333790","amount":{"value":"102800.00","currency":"IDR"},"latestTransactionStatus":"00","transactionStatusDesc":"SUCCESS","additionalInfo":{"refundHistory":[]}}

Private key (PKCS#8 PEM) Public key (SPKI PEM)

X-SIGNATURE (base64)

RoJnP2tH/YiOhHM/lMVBMSAuzRmS8VrWdIy04Qqyb56daV7oWFMFoMMzqnjQ+q0MIUalYgU094GWQnCx2c29xb1kkqHhv2+iJ9xl6NjGmFGYqyvcKvUDAV83Y1Mw9JnsEcjcupdGw9/MRv/mm2GMrQ+BCZGfc4a46JDyPZbcY294vDGqs5rFBN6iYer5ro4cAQGo9hET2G82Y+j50vCyO/79GFE4vB1rvtu6PK2Bxi+vTYV8k7P7PS8tOPWM2O+kjiVWjwvLR99Botou+a8sxlQqZaihfWMKcByzV+Lgkr9cptpjys+1NIRWT1ad/sJBSLHyldzC3q2oRn5z5oZmyg==

String to sign

minify(body) lowercase(hex(SHA-256(minify(body)))) HTTPMethod : EndpointUrl : hash : X-TIMESTAMP

Result

Signature / verdict

About this tool

A workbench for the asymmetric signature in Bank Indonesia's SNAP BI standard, the same scheme Midtrans uses for payment notifications. It builds the string to sign from the HTTP method, endpoint, a SHA-256 hash of the minified body and the X-TIMESTAMP, then signs it with an RSA private key or verifies it with the sender's public key. Both operations run in the browser with the Web Crypto API.

Questions

What exactly is the string that gets signed?: HTTPMethod + ':' + EndpointUrl + ':' + lowercase(hex(SHA-256(minify(body)))) + ':' + X-TIMESTAMP. The method is upper-cased, the body is minified JSON, and its SHA-256 is written as lowercase hex. Join the four parts with colons and sign that exact string.
Which key goes where?: Signing uses the private key of the sender. Verification uses the public key of the sender, not yours. For a notification you received, the sender is the payment provider, so paste the public key they published.
Why is the body minified before hashing?: The signature must not depend on cosmetic whitespace, so both sides agree to strip it first. JSON.stringify(JSON.parse(body)) removes the formatting and the receiver hashes the same compact form. If the body is not valid JSON it is hashed as typed.
Is this the same as SHA256withRSA in Java or Node?: Yes. Web Crypto's RSASSA-PKCS1-v1_5 with SHA-256 is exactly SHA256withRSA, so a signature made here verifies in Java, Node or any SNAP BI library, and the other way round.
Can I use a production private key here?: Technically yes, but do not. This is a public web page, so paste a test key, or press Generate key pair to create a throwaway 2048-bit pair and try the flow end to end.

SNAP BI Asymmetric Signature