# For Cognito USER_SRP_AUTH - how to calculate PASSWORD_CLAIM_SIGNATURE to respond to ChallengeName: "PASSWORD_VERIFIER"?

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This knowledge article describes the calculation of `PASSWORD_CLAIM_SIGNATURE` for the case of `ChallengeName: "DEVICE_PASSWORD_VERIFIER"`.

• Let PASSWORD_CLAIM_SIGNATURE = SHA256_HMAC(K_USER, DeviceGroupKey + DeviceKey + PASSWORD_CLAIM_SECRET_BLOCK + TIMESTAMP), base64-encoded
• Let K_USER = SHA256_HASH(S_USER)
• Let S_USER = (SRP_B - k * gx)(a + ux)
• Let x = SHA256_HASH(salt + FULL_PASSWORD)
• Let u = SHA256_HASH(SRP_A + SRP_B)
• Let k = SHA256_HASH(N + g)

What is the equivalent calculation of `PASSWORD_CLAIM_SIGNATURE` for the case of `ChallengeName: "PASSWORD_VERIFIER"`?