GPG key Error while bringing up the docker

Got the following error while running docker-compose build

W: GPG error: http://archive.ubuntu.com/ubuntu precise-updates InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 49976Egf897D05B6
E: The repository 'http://archive.ubuntu.com/ubuntu precise-updates InRelease' is not signed.
W: GPG error: http://archive.ubuntu.com/ubuntu precise-backports InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 49976Egf897D05B6
E: The repository 'http://archive.ubuntu.com/ubuntu precise-backports InRelease' is not signed.
W: GPG error: http://archive.ubuntu.com/ubuntu precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 49976Egf897D05B6
E: The repository 'http://archive.ubuntu.com/ubuntu precise Release' is not signed.

Here is what my Dockerfile looks like…

FROM php:7.2-apache

RUN apt-get -y update && apt-get install -y software-properties-common

RUN add-apt-repository -y "deb http://archive.ubuntu.com/ubuntu precise universe" && 
    add-apt-repository -y "deb http://archive.ubuntu.com/ubuntu precise main restricted universe multiverse" && 
    add-apt-repository -y "deb http://archive.ubuntu.com/ubuntu precise-updates main restricted universe multiverse" && 
    add-apt-repository -y "deb http://archive.ubuntu.com/ubuntu precise-backports main restricted universe multiverse"

RUN apt-get update && apt-get install -y --allow-unauthenticated
      software-properties-common 
      python-dev 
      python-pip 
      s3cmd 
      cuneiform 
      poppler-utils 
    && apt-get clean 
    && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* 
    && docker-php-ext-configure pdo_mysql --with-pdo-mysql=mysqlnd 
    && docker-php-ext-install 
      opcache

The error pops on 3rd step (while running apt-get update).

Source: StackOverflow